I've used 4' agricultural fencing with 4"x2" mesh, attached to T-posts every 8'. We installed this when we rented, since we needed a fence but could not do anything permanent. It cost about $300 (which included some tools we needed such as a wire cutter and post driver) and we fenced in 2600 square feet. Probably could have done it cheaper but it was one of those things where I woke up one morning and decided to do it so we were limited on what supplies and deals were available. It held my GSDs fine. Coke would dig under it to get out so he was either supervised or on a tie-out inside the fenced area (he's always been tied out so he was used to that).
Liesje & the K9s
Nikon (GSD) U-CH SG SchH1 KKL T1 FO PA TFE-I FDCh-S CL1-R UJJ U-CA HIT TT CGC, free reign semi-retiree
Coke (All-American), couch warmer extraordinaire
Indy (All-American), flyball star in training
Rainbow Bridge Kenya (GSD) U-CH FO OB1 CL1-R CL1-F RA HIT TDI TT CGC