Lead generation companies are pretty much all cut from the same or very similar cloth.
There have been plenty of debates on this site about lead generators, a quick search will probably give you all you need to know.
However, my feeling is that paying for leads upfront is not a way to sustain your business. If someone offers me a lead where they only get paid when the escrow closes, then I am willing to listen.
Your best lead generator is YOU.
R