No reason to order online if you are looking for cultured liverock. Plenty available here. Most of the stores stock various forms of Real Reef (my favorite man-made alternative, FHI rules) including tonga branches. Reef Culture has the largest bins of rock, overall, but I think all the stores have some... Aquarius has (had?) some really choice pieces from a big tank breakdown.
If you want it on the cheap just make a WTB Liverock thread and I'm sure you will get plenty of hobbyist responses. Plenty of people with cooking bins in their houses (for some reason, lol)