As you have probably noticed from other posts here, you can get some excellent bargains from charity shops, and these can easily form the basis of a costume. Most towns have somewhere selling fabric by the metre, and these often have a bin with remnants.
As you will have noticed (if you have attended any Steampunk events), you MUST have a pair of goggles. If you are to be a Zeppellin engineer, or indeed involved in the maintenance of a steam engine, then the most basic goggles - such as welding goggles - will do for a start. If you intend later to be the dapper 'Man About Town', then you might consider upgrading to something a little more outré.
I've recently bought a copy of Steampunk Gear, Gadgets, and Gizmos : A Maker's Guide to Creating Modern Artifacts by Thomas Willeford; I've found it full of good ideas. Jeff Vandemeer's Steampunk Bible - An Illustrated Guide to the World of Imaginary Airships, Corsets and Goggles, Mad Scientists, and Strange Literature can also give you some inspidration. I bought both from abebooks.uk.
Charity shops can be a source not only of costume items, but of accoutrements too. Kitchen equipment can be repurposed for your 'weapon'. Just hope, when you visit, that some other Steampunk hasn't been in before you!
