Perlite is the most expensive product in your mix of ingredients for hypertufa. If you just want to experiment, just get the smaller bag, that you usually find in the garden department... but for cost savings, you can get the bigger 2 cu. feet or even 4 cu. feet bags of perlite. You can get the 2 cu. feet bags at Home Depot and it's made by Therm-o-Rock. The bags are green in color and I usually pay about $17 for this size bag. I recently found a local supplier, where I can buy the bigger 4 cu. feet bags for about $25. You can also use vermiculite, but it's usually more expensive. Good luck!

Unfortunately Home Depot here doesn't sell anything like that anymore for the season. I went earlier this week and the garden center is closed. They have nothing but 1000 snowblowers they shipped in and are only selling winter things now (What the hell!?) And they are selling these things at full price, lol.

So any summer stuff I need to buy in the summer has to be purchased elsewhere it seems.

Try a garden center or farm store. They will have large bags of perlite at a better price

I was able to obtain an enormous bag of coarse perlite for about $12-15 at the local farmers co-op last year.