Might i suggest the team 639 method?
http://www.startateam.com/639/photos.php?pageid=1
each 'buck' is worth approx 1 slice of pizza. Of course the market should determine this by itself- depending on peoples willingness to drill holes they might be worth as much as 2 slices and a drink.
I figure you could get by on a smaller battery if your robot simply hooked onto your team-mates until it could get close enough to latch onto your opponent. It could be a blood sucking robot!
In the end dropping components is usually the only way to lose more then 5 pounds... it sucks but sometimes its what has to be done.
Greg