If you don't mind sometimes sub par quality, but cheaply priced, SirToys.com has cool KO's.

 

Oh I forgot, other than MMC / FP / MT / IF and DX9, another very nice option below 100$ is FT Insecticons for around 85$/ea member. Maybe try out FT Grenadier that is coming out soon, and see if you like it. It will have plenty of die cast in it, and chrome, heavy little guy.

I would say definetly start with either MMC Reformatted line (Spartan, Commotus, Anarchus) which will be released from sept - dec, or FP Combes Robin (or regular version for better price), or FT Grenadier (I think will be released in sept)

The reason is, the legends figures don't have that much of a transformation to them. They are very nice, and I love them, and it is much easier to start collecting these and keep on adding and I highly recommend Iron Factory / DX9, but I want you to feel some of the real transformation and much better bot / alt modes out there because of the increased scale.