how much and where depends on who/what you know.
i paid £320 for my ecu an dpart loom running wasted spark, so no edis, just a coil pack.
you have to make a loom from a frst/2i/3i/zetec engine loom, then you need to start mapping and get the startup settings right, this is the hardest part IMO.
you can go to M-tech, although i've heard mixed opinions.
i got it off a guy on xrtwo.com forum called 'steve'.
they'll probably cost more due to the drop in the pound over the last year.
you can get a lesser version, but the MSIIv3.0 is the best and can run on extra mode, so 16*16 fuel tables, much more precise control of fuelling then.
lesser models can be bought for around £200, slower processor though.
ideally you need to get a wideband afr setup too, innovate do one for less than £200, then you can map it whenever you want after any changes, such as cam,turbo, injectors etc.

edited: efiextra.com is where i would recommend an ecu etc.