If you wait for Xray's new chassis to hit the shops I'm sure the best deal will be on old Xray stock still in the shops...
I think the kits you're looking at are in the £380 area, I don't know if you'd get one for £350... I guess if you're buying everything else you can haggle for a discount but the margins are so slim on these shops can't offer too much.
I'm with you on the used philosophy and the hidden gremlins but as was said earlier a lot of people will buy a chassis, do a few races with it and then decide don't like it so much and move it on. It's generally experienced racers doing this and as has been said they're the ones who look after their cars. You really should delve deeper into this before you discount the used route altogether. I picked my Agama up only a few races old with a huge spares package for an absolute bargain, I felt a bit guilty when I met Ben and gave him the money actually...
Get on MB, take a look at their used section, I've just looked quickly, there is a JQ THE car for £210, 2x Losi 2.0 for £250, Hobao Hyperstar for £210, no Xrays though
It could bring your final cost down by at least £200 and with the fact you have a radio too I reckon you could get up and running for £600 with good stuff.