If it's a 'fender' style bass with passive, single coil pickups (long and thin instead of long and fat), or a P bass or copy then the pot will be 250kΩ Log (A type), if it's got humbuckers then it'll most likely be 500kΩ Log.
You can get them from Maplin for about a pound or a better quality pot from http://www.doctortweek.co.uk for roughly half the price. I'm not sure that there is a way of replacing volume pots without soldering.
If you're unsure about the work involved then I'd recommend taking it to a reputable technician (or see if there's a fellow Basschatter nearby who has done this soret of thing before). It's not a complicated job, but it can be a bit daunting if it's your first attempt - and there's a deadline involved.
Hope this helps.