Depends which Focus Rs your talking about! MK1 read below:

Yes the standard ECU can be mapped, i know Motorsports Development have done a couple. I believe a live map from them starts at about £500

Bluefin is the name for the handheld device Superchips currently sell, you get the unit plug it in and load the map and its done believe the cost of this is around £300. this is available for mk1 and mk2 RS's

Other companies do maps for the Rs as well, Dreamscience are good but Pete at Demon Performance Centre: http://www.demonperformancecentre.co.uk/ can also do remaps and most mk 1 FRS owners take their cars to him he does mk2's as well though, great prices and great knowledge and doesnt rip you off.

Mk2 FRS have alot more plug and play style remaps: Revo, Code Red, Mountune, JR racing, Jamsport, Sitech, thats just to name a few sure there are loads more!

Aftermarket ECU is not something ive looked at unfortunatly so couldnt give any advise on this!