£150 is a fair budget for a complete outfit. As I said before the tie is the thing people notice, make sure its for the right reason. A classic style suit is a must ask yourasel if it will work for wedings, funerals if it does thats the one. If your slightly unsure, dont buy it, you need to be comfortable in it (I don't just mean the fit). Shoes and socks again cleaned per interview. Avoid paterned shirts, that clash with your tie or suit.
Get yourself over to the designer outlet in Castleford, there is a shop there that have suits, ties, shirts and shoes all in your price range, I got a rather nice gucci tie for about £15-20 rather than the £65-95 at harvey nick's. 99.99% of interviewers wont tell the difference between a £100 suit and a £1000 one, but will notice if your tie isn't silk. Learn how to tie a nice knot rather than a schoolboy wrap round push through afair, if unsure ask an assistant only if theirs is well tied though.
One point worth making is when you get back home, take it off imediately, and put it on its hanger. No making cuppas or slouching around in it, save the shoes just for interviews until you get a job. Basicaly keep your new suit new, you will look and feel better for it.