Hmmm well realistically, I'd make a list of possibles... then find out what cars are available with a short turnaround (from ordering to delivery) before wanking off over the online car builders mate. No point getting all geared up for a tidy spec BMW 3-series then finding out that because it's a new model, it's got a delivery date 18 weeks down the line.
Volvo V70 D5 R-Design, think they're <35k with a few options... with a haggle, it might be down around ~30k.
Cheers,
Grant