A vendor quote for an ordering system arrives as a per-user or per-order figure, annualized, with a discount for paying up front. It is a clean number. It is also, in most replacements, somewhere between a third and a half of what the first year costs you, and it is the only part of the bill that shows up as an invoice from the vendor.
The rest arrives as your own people's time, a second vendor's time, and the cost of running two systems at once while nobody is quite sure which one is right. None of that is hidden exactly. It just does not appear on the quote, because the vendor is not the one paying it.
Below, in the order the costs actually hit, is what to price before you sign.
1. Getting your data out of the old system, which is your problem
Export is the first task and the one most often assumed away. The question is not whether the incumbent system can produce a file. It usually can. The question is whether the file contains what you need in a form something else can read.
Customer-specific pricing is the usual casualty. So are contract terms, credit limits, shipping defaults, tax exemption certificates, and the mapping between your part numbers and a customer's part numbers. These often live in fields the original vendor added later, or in free-text notes, or in a spreadsheet one person maintains. Finding out which happens during export, not during the sales cycle.
Ask the incumbent, in writing and early, what the export includes and what it omits. If the contract gives them no obligation to help, assume slow and charged by the hour. Budget for a cleanup pass: somebody has to decide what a duplicate customer record means and whether a 2011 order needs to come across at all. The IRS sets the rules on how long business records have to be retained, which means the answer to "can we just not migrate the old orders" is often no, or at least not without keeping the old system readable in archive form.
2. Integration, counted per connection and not per system
The licence covers the platform. It does not usually cover making the platform talk to your accounting package, your warehouse, your freight rater, your tax engine, or the EDI feed from your three largest accounts.
Price integration by counting connections, not by counting systems. Each one has a direction, a frequency, an error-handling path, and someone who owns it when it breaks at 6am. Some will be covered by a prebuilt connector that works. Some will be covered by a prebuilt connector that works for the standard configuration and not for yours. The remainder are custom, and custom means a statement of work from an implementation partner.
When you compare a b2b ecommerce platform against an incumbent you already run, the honest comparison is total connections times effort per connection, plus whatever ongoing maintenance each one carries.
Get the partner to quote per connection. A single blended implementation fee makes it impossible to see what you are being charged for the hard ones.
3. Running both systems at once, for longer than planned
Almost nobody switches on a Friday and off on a Monday. There is a parallel period, and during it you pay for both systems, plus the labor of keeping them in agreement.
This is where delay stops being recoverable. A parallel run that was scoped at six weeks and lands at five months does three things: it doubles the subscription overlap, it burns the goodwill of the staff doing double entry, and it gives everyone a working excuse to keep using the old system. Once customers and reps have learned that the old way still functions, pulling the plug becomes a negotiation rather than a decision.
Set the cutover date before the project starts, make it a date rather than a milestone, and price the overlap month by month so the finance side can see what slipping costs. If the overlap is going to extend, extend it deliberately and decide what the new end date is in the same meeting.
4. Training, and the quieter cost of your customers relearning
Internal training is the visible half: sessions, materials, a few weeks of reduced output while people look things up. Price it as hours at loaded cost, not as a line item from the vendor.
The half that gets missed is on the customer side. If buyers place orders through a portal, they have logins, saved carts, reorder lists, and habits. A replacement resets some or all of that. Expect a spike in phone and email orders during the transition, which lands on the same inside sales team already learning the new screens. Plan for temporary coverage during the first two billing cycles after cutover, and tell your largest accounts the date in advance rather than on the morning.
5. The year-two bill, which is not the year-one bill
First-year pricing often includes an implementation discount, a promotional rate, or a user count based on who you have today. Read the renewal terms before signing: the uplift cap, what happens when order volume crosses a tier, what a sandbox environment costs, and whether support at the level you were shown during the demo is the level you actually bought.
Ask what a mid-term addition costs. Adding fifteen users in month seven at list price, when the original hundred were discounted, is a surprise worth finding now.
Then total it: licence, migration, integration per connection, overlap, training, and the year-two number. That figure is the one to compare against staying put.
The projects that come in near budget are not the ones with the cheapest licence. They are the ones where somebody wrote down the cutover date in week one and treated every other cost as a consequence of hitting it.
