I'm trying to understand this. So you have an alt rogue with professions that don't benefit it at all so you're trying to buy gear off the AH but it's too expensive? I got a warrior up to level 35 and for the majority of that there was virtually nothing for low to mid levels. The stuff I did find was maybe 1 plat at most for blue 2 handers.
What I did to gear up and battle my way through wf's is to visit the rare planar vendor every 5 levels. Each one has one epic and one blue quality piece for your level and the planarite cost is negliigible since you already have a 50. If you need sourcestones you can do it on your main and send vouchers to your alt. I had a full source engine at level 5 filled with lessers that cost less than 50 planarite apiece.
The best thing to do though if you don't want to hit up the rare planar goods guy every five levels then ask your guild to craft something for you. That is what they are for, for like minded people to play together and help each other when needed.