Pythons are craaazy cheap at my local Walmart compared to my LFS. My LFS has always been expensive (especially on fish, but they are A++ quality), but it's like $67 for the Python that I needed, and at Walmart, a 25 footer was only $15.99. That's why I have it now. ^^ I also get most of my food at walmart, since ours just started carrying most all of the Hikari foods, except for the sinking formulas.
Home Depot of course, Sand for $3 for 50lbs, gravel is $2 for 50lbs.
Michaels I recently discovered has a good amount of silk plants that are very useable in the aquarium, as does most dollar stores.
For larger rocks, and slate, rock quarrys are paradise. They usually sell rocks by the TON, so if you just take out a couple handfuls of rocks, they rarely charge you more than $5 if they even charge you at all.