I see the guy above this post only ever wrote that one post, guess this was not the site for him.
Anyway, one of the best tips I can give collectors is to check their local thrift shops and salvation army outlets. You will almost never find a complete transformer there (I never did) but its a great place to find parts and placeholders. There is a junk market not too far from where I am which I visit once a month, and its made up of a bunch of small stalls where people sell the junk they find. I was able to find a nearly complete ROTF Leader Megatron for 5$ and a 90% complete Leader Deep Dessert Brawl for 10$.
If anyone has a Hasbro RID Rail Racer and is looking to sell it, let me know.
And if anyone cares for these, I have an extra Arms Micron 27 Ultra Magnus up for grabs.