been a while since i was 17!! but have just sold a vw transporter (loverly van) and bought an 03 reg ex postie vauxhall combo that is mint and only paid 3k with 35k miles, my sherco fits in no probs, has rubber floor is lined and has 6 tie down points, it drives like a car because it is, is very cheap to insure and run + being 17 you could fit large alloys + other corsa bits ect ect, why have anything bigger!!.
on a lower budget my brother in law has an older shape combo and he fits his sherco in the back no probs (and that has an LPG tank in the way!).
if you remove the false floor + bulkhead in an old combo (a few pop rivets) you can actually get two bikes in the back ive seen it done!
insurance is gonna be a killer on anything tho but bite the bullet mate we have all been there, hope this helps.