I sold mine for £300 plus a swap.
If you get a second hand one, you will need to get the keys from your car coded to the new ECU, £35 at Honda, but not all garages will do this, so call around first. Then, the existing map on your new K100 will be mapped to teh old car and its mods, so it wont be running properly. Of Course it depends on your mods, if its similiar to the old car then it will be close.
Plug and play? Like I said all depneds on teh mods your running and your confidence in the map installed on teh ECU, but yes, it will lower your VTEC engagement and give you some extra grunt down low. Maybe even a few more horse's top end.