You get what you pay for. Autocom always come out top of the magazine tests but a bike to bike set will cost about £200 per bike plus the radios. VOX is the system you are thinking about, it starts transmitting as soon as you start talking. Systems without VOX cost a bit less. Radios cost from £130 a pair for cheapies to £180 each for decent Kenwood or Motorola kit.
From experience i think that cheap kit is a waste of money. The good kit actually works!
www.autocom.co.uk