I've got an autocom aswell - a great piece of kit.
Mine is hardwired to the bike, however they also do a battery powered version.
Cheap kits are ok, however their limitations are usually:-
1) Relatively uncomfortable to wear (Autocom use decent quality slimline stereo speakers mounted in the lid rather than ear pieces)
2) Not always VOX operated (VOX setting on the Autocoms is adjustable)
3) Poor sound quality especially at 'motorway speeds' (no problems talking to my pillion at speeds that I dare not mention on this forum
)
4) Poor range - this is dependant on transeivers - see below
For bike to bike there are two elements - one is the headset/mike & interface (i.e. the autocom bit of kit) - the other is the transceiver - if you can afford an autocom and a decent quality (i.e. around £50 upwards) transceiver than you should have no real problems talking to each other at 'silly speeds' with a range of around a mile (depending on buildings etc)
HTH
Matt