The cheapest Valks you can get are Hi-Metal VF-1s. Those usually sit in the $110-150 range, I don't think I've ever seen them for anything less.
I got my VF-4 for about $130-140.
If you want a decent transforming Macross toy you'll never find one below $100 unless it's broken.
Do yourself a favor and drop a little more cash, you won't regret it, most of these figures are truly worth it.