£300 should be enough for all equipment, not sure on a 3x2x2ft but you can pick up 4ft vivariums for £100 these days if you look hard enough, looking at around another hundred for the rest of the equipment including a thermostat, again if you shop around may find a good deal, although if using a heatmat, mat stats are relatively cheap in comparison to fancy stats with magic eyes and all the non essential gubbins you don't need.
I would personally recommend a corn snake but that's just my opinion as i think they are great, and as stated they are great feeders, placid in most instances, and have great character so would make a good choice. Also if you are looking for a colourful snake then corns are great due to the huge range and availability of morphs on offer with most costing under £100. As in any case and i'm sure you will, get plenty of research done before committing, but i'm sure you will be fine. Hope this helps, please anyone correct me if my info is of no good, don't want to be giving out false advice.