Ok, bit of an update:

I've put off starting the build until next easter/ summer, which gives me plenty of time to source cheap parts. My main sticking point atm is drive motors, with a second lawn mower starter motor not forthcoming (The guy I was gonna get them off didn't have any). I'm going to keep an eye out on eBay for any suitable cheap motors. Hopefully with a year to browse I'll find something half decent; I'm currently leaning towards some wheelchair motors to keep gearing simple.

I'm also looking at scratch building the ESC again, as the cheap ESCs I was looking at before were missing proper gate drivers which makes them unusable for this even with hacks. Having done a bit more research and reverse engineering various ESCs such as the TZ85, I've been working on a design for a dual ESC capable of ~40A continuous @ 40V which is pretty simple and cheap on parts (~£20) and can easily be upgraded to more amps with different/more FETS, though if it's just wheelchair motors, 40A should be fine...

As for weaponry, I'm still going for the forked lifter, however I'm thinking of using a cable/ rope winch with block and tackle pulleys along with tensioning springs to stop it all getting tangled... largely because it's cheap, light, and it'll look cool though the polycarb; I'm aiming for a bit of a steampunk or post apocalyptic look for this one (might get some riveted corrugated iron or something over the polycarb in places for that Fallout 3 look :P )

I've decided to up the budget to £100 just so I can get some parts that'll work for more than one fight. As I say only thing I'm really missing is drive motors, but there's always plenty of small parts which add up quick. My aim is to make something that may be a bit useless, but is fun for the crowds and as solid as a rock