As you say, "classy" is somewhat subjective. Have had a quick browse of both ebuyer and Scan, and Scan seems to be the better option for cases at the minute. I'd consider:
Zalman T5 £17.94
Cheap and sleek black front, although it sports funny power-bulge sides that I'm not personally so keen on. Good internal layout with bottom mounting PSU, plenty of fan mounts and front USB 2 and 3.
Antec VSK3000 £21.98
Very traditional plain black tower case, with top mounted PSU and USB 2 ports only. It's like someone took a mid 90's beige box and painted it black
Sharkoon CA-M £43.80 £32.00 at amazon
Possibly the most marmite selection looks-wise, but I think it looks great. I also like the layout, which mounts the PSU next to the motherboard, over the CPU socket. It does mean you get reduced clearance for your cooler, but if this is a "free" build I'm guessing there's a fairly stock CPU cooler in there which will be fine. Another case with front USB3 as well as USB 2, the only potential issue is the lack of an optical drive bay.
EDIT: just found the Sharkoon in both
BLACK and
SILVER for £32 on amazon - I think I like it in black even more