Two quotes land in the same inbox on the same Tuesday. One says “PRTG 500”, the other says “75 devices”. A third vendor wants to know how many “nodes, interfaces and volumes” you have before it will name a number. None of these units are the same thing, and that is exactly why so many monitoring purchases go over budget in year two. This guide translates the four licensing models you will meet into one currency: what a real network actually costs to cover.
A note on the numbers. Every price below comes from a deliberately made-up price sheet so the arithmetic is easy to follow. They are not any vendor’s list prices. Use the method, then plug in the figures from your own quotes.
The four licensing models you will run into
| Model | What you pay for | Typical example | What makes the bill grow |
|---|---|---|---|
| Per sensor | Individual metrics (a ping, a port’s traffic, a disk’s capacity) | PRTG subscription tiers | Monitoring more things on the same device |
| Per device | Each monitored box, with its interfaces bundled in | ManageEngine OpManager | Adding devices, regardless of depth |
| Per node / element | Nodes, sometimes plus interfaces and volumes counted as separate elements | SolarWinds NPM | Nodes and, in element models, every port you watch |
| Per network device / endpoint | Infrastructure gear only, or every managed endpoint, usually per month | Auvik (network gear), NinjaOne (endpoints) | What the vendor counts as “billable” |
The do-it-yourself baseline, Zabbix, the open-source edition of Checkmk and LibreNMS, has no license fee at all. Its cost shows up as server hardware and staff hours instead, which we treat as a real line item below.
Our hypothetical price sheet
To compare like with like, we invented one price per model:
- Per sensor: 500-sensor tier at $2,000/year, 1,000 at $3,600, 2,500 at $7,800, 5,000 at $14,000.
- Per device: $25 per device per year, interfaces included.
- Per node (element-style): tiers of 250 elements at $4,000/year and 2,000 elements at $18,000/year, where a node, an interface and a volume each count as one element.
- Per network device: $10 per billable infrastructure device per month (switches, routers, firewalls; access points counted too in this example).
Worked example 1: a 60-device office
Our first site is a single office with this inventory:
| Device type | Qty | Est. sensors each | Sensors |
|---|---|---|---|
| Firewall | 1 | 12 | 12 |
| Switches (about 20 used ports each) | 6 | 26 | 156 |
| Wireless access points | 10 | 3 | 30 |
| Hypervisor hosts | 2 | 15 | 30 |
| Virtual/physical servers | 14 | 8 | 112 |
| NAS / storage | 3 | 8 | 24 |
| Printers | 4 | 3 | 12 |
| UPS units | 2 | 4 | 8 |
| Phone system | 1 | 3 | 3 |
| IP cameras (ping only) | 17 | 1 | 17 |
| Probe and system health | — | — | 5 |
| Total | 60 | 409 |
Now the four bills:
- Per sensor: 409 sensors plus 20% headroom is about 490. That squeezes into the 500 tier at $2,000/year, but one new switch would push you over. Realistically you budget for the 1,000 tier: $3,600.
- Per device: 60 × $25 = $1,500/year.
- Per node (element-style): 60 nodes + roughly 130 monitored interfaces + 40 volumes = 230 elements. Fits the 250 tier: $4,000/year, with very little room to grow.
- Per network device: firewall + 6 switches + 10 APs = 17 billable devices × $10 × 12 = $2,040/year. Servers and printers are not covered in depth at all, so you would need a second tool for them.
At this size the differences are small in absolute dollars. What matters more is the shape of the curve: the per-sensor bill jumps in steps, and the jump arrives the day someone adds switch-port traffic monitoring for every access port.
Worked example 2: a 600-device, five-site organization
Scale the same mix by ten and spread it across a head office and four branches. Two things change beyond multiplication: every branch needs a remote probe or collector, and the core network gains a few chassis switches with hundreds of active ports.
| Model | Count | Hypothetical annual cost |
|---|---|---|
| Per sensor | ~4,100 sensors + remote probe health ≈ 4,150; with headroom, the 5,000 tier | $14,000 |
| Per device | 600 devices | $15,000 |
| Per node (element-style) | 600 nodes + ~1,400 interfaces + ~400 volumes ≈ 2,400 elements; exceeds the 2,000 tier | $18,000 + a second tier or an upgrade quote |
| Per network device | ~170 switches, routers, firewalls and APs | $20,400 |
Per sensor now looks competitive, but only if you are disciplined about which ports you monitor. Per device stays flat and predictable. Element-style licensing punishes interface-heavy networks. The per-network-device model is the most expensive line here yet covers only the network layer, so in practice it gets paired with a server monitoring tool.
Hidden costs that do not appear on any quote
- Server and OS licensing. Self-hosted platforms need a Windows or Linux server, and some need Microsoft SQL Server, which can cost more than the monitoring license at small scale.
- Add-on modules. Flow analysis, configuration backup and IP address management are sometimes separate SKUs. Ask for them by name.
- Renewal uplift. Year-one discounts are common; ask what year three costs.
- Staff time. For the DIY tools this is the main cost. Budget realistic hours for templates, upgrades and alert tuning, at your loaded hourly rate.
- Remote sites. Probes, collectors or polling engines may be included, or they may be charged per site.
Common mistakes when comparing quotes
- Counting devices when the vendor counts sensors. Rule-of-thumb multipliers vary wildly by device type. Use our PRTG sensor estimation guide before you pick a tier.
- Ignoring growth. Price the license you will need in 24 months, not today.
- Comparing a network-only tool with a full-stack one. Make sure both quotes cover the same scope.
- Skipping the trial. Real sensor and element counts only appear once discovery has run on your network. Our 14-day trial plan shows what to measure.
Where to go next
If the licensing model has already narrowed your list, the head-to-heads help: PRTG vs SolarWinds NPM is a per-sensor vs per-node story, and PRTG vs OpManager is per sensor vs per device. For a scored shortlist by company size, see network monitoring for small business and enterprise network monitoring. Our methodology explains how we weigh total cost against features. When you are ready to write it all down for vendors, the requirements checklist turns these questions into an RFP.