For cheap but solid, the Byrd line by Spyderco. You're going to hard pressed to find folders that big - I think the biggest they have is a 4". As for the other requirements, I think you may have to have a little flexibility.

http://www.knifecenter.com/kc_new/store_detail.html?s=CS62KG
http://www.knifecenter.com/kc_new/store_detail.html?s=CS21S
http://www.knifecenter.com/kc_new/store_detail.html?s=CS29XXC
http://www.knifecenter.com/kc_new/store_detail.html?s=BM741BK
http://www.knifecenter.com/kc_new/store_detail.html?s=BM760BK
http://www.knifecenter.com/kc_new/store_detail.html?s=BM13220

Mainly, just look through every page...