Most of the folks who use software use BidNav. I used it for a couple months with reasonable success but honestly looking at how experienced folks construct their lines and seeing what has and hasn't worked is equally good.

If you want to save $50/month when you're on first year pay your best bet is to find experienced bidders willing to share. You'd be amazed at how many folks love talking about how they bid and showing their standing bids to you when you're flying.