Heres a few idea for Mech costumes we used in Decay of Nation IV
We also had our tank turned APC.
Everyone of these ideas where very inexpensive to build, however the more time spend, the better the suit.
Black Sun "aka Jazz from the Grey Knights" was in costume R&D was 2 months, build time 2 1/2 weekends
Saloon in our true mech Sentinel MkII was a redone project from Decay of Nation III. R&D 6 month(between the 2 years of use) build time 3 months
Oh and the Sentinel did have a (dog leg) style leg armor. Minor foot problems but otherwise all suit run wonderfully
The two mech suits: Termie 4 month R&D 1 month build time. Fluffy Death borrowed R&D from Termie and build time 4 days
Keep and eye out for next years projects