Does a replacement ECU need programming to the car?

So, not sure from your question if you have had the work done or not, but it won't affect the answer.

The new (or good second hand replacement) will need to be programmed to the vehicle as it needs to know the addresses or identity of the other components to function correctly.

In fact, some cars have to have the dash, lock control and ecu all sold together as re-programming is not always successful - and you see adverts for "sets" on selling sites for exactly this reason.

As to the price, well, difficult to say as prices vary for labour etc between country / location and who did the work.

If it is working now and the vehicle still has value then you get what you pay for.

£700 would be quite a lot for a used ECU for one of those if it is just for the actual hardware (a plain used unit that hasn't been refurbished or anything should run around £50-100, adding in another £100-150 if it has been refurbed). If the invoice is including labour etc to fit and re-program the unit to the car then that would seem to be a lot more reasonable if a little bit on the high side.

A "new" ECU will almost certainly need programming to the car - if nothing else there will be anti-theft measures such as the immobilizer to consider and potentially other systems in the car for it to be configured with. The actual time needed to swap and re-program is relatively small (maybe 2-3 hours) but many independent garages will have to charge more than just this since the equipment to program ECUs is generally not cheap and they will be looking to recoup that investment.

A used ECU would have to be programmed to your vehicle, depending on make and model it can be as simple as using a diagnostic tool to program it or a lot of times it can involve swapping the contents of the internal memory from the old ECU to the new one which isn't a job for the average garage.

If it is just a case of programming with a diagnostic tool there should usually be a flat rate for this. In the UK this I would say around £50-75 to program and verify a ECU.

If it requires physically swapping the memory contents this is a job that usually requires a specialist as the ECU needs to be opened, the memory IC will then have to either be soldered or read/wrote with a very expensive tool. A Auto-Electrician or specialist would usually charge between £50-£200 depending on what ECU / Memory it has. This usually excludes removing the ECU from the vehicle (unless it is extremely accessible)

ECUs can be repaired and usually this is the best option, there are dozens of companies in the UK that usually charge around £200 to repair and recondition your ECU and will have a life time warranty. This is good because the ECU will be plug and play meaning no programming charges, some companies will even provide instructions on how to remove and replace it.

Yes, always. Even if it's the same model. You have 2 options, either you buy it virgin and code it yourself for instance here, or you can buy it already coded, and ready to plug and play here. And always, be sure you got the exact same reference. (number by number) Otherwise it won't work:(