Amazon had the best prices that I found. I bought a flat size one for like $20 and then bought a 4 foot by 4 foot on there for about $50
Oh..and just another technique I use..and quite honestly, its by FAR the best method I have found.
I put my seeds in cups like many folks on here. Then, I put them in the oven and turn the oven light on (no, I don't turn the OVEN on
)
This keeps the temp right around 85 degrees and things germinate like mad
Example: I planted cayenne the other day. Had on a heat mat for a week now, nothing. Those seeds typically germinate quickly. Well, yesterday, I moved them all into the oven and today I had 5 germinated and had about 1/4" root already.
Only other advice..put a sticky note on the button or dial that turns the oven on that says "SEEDS" just so you don't accidentally forget about them and turn the oven on preheat
that my friend will cook your seeds faster than you can say SOB!