Ah yes, the immortal issue. Sadly I don't think there is such a thing as decent, cheap, steamy wear!
Looking at what your avatar is wearing isn't a bad starting point.
The second issue of Steampunk Magazine has a nice article on steampunk fashion you could read for inspiration.
Failing that, check out any local vintage fashion shops or army surplus places for anything that catches you eye. You might be in luck!
One chap I saw pull of something cheap and respectable, was simply wearing smart trousers, a smart shirt and suspenders and a rather dashing newsboy hat or a bowler.
I got my bowler hat from a fancy dress shop.
biggrin