I too felt the burden of aspen prices, and although I love using it, I wanted another option. I went to a local animal supply and feed shop and decided to test out the only option they had there.
To my surprise, it's worked pretty well! I've been using Eco pine wood pellets, which are compressed wood. It's marketed as bedding for livestock animals like horses. If I had to buy enough to fill a stall I might be in trouble, but for the snakes it works great. The nicest thing about the compressed wood is that it expands when it gets wet. This is awesome because the substrate completely absorbs the water, and once it is one expanding it dries out again. It doesn't seem to get too dry though. If you leave the lids on your tubs it will not dry out completely.
I bought two decent sized bags of this stuff for around $6 or so, I can't remember exactly, it's lasted me pretty long. It's about time to restock. I'll check the prices for you and perhaps get you a good name brand if you're interested.
This isn't a great picture, it was taken after I pulled up the paper towels I lay the substrate on to find this guy, but it shows what the pellets look like before and after they've expanded.
Oh, I've been using Timothy Hay as well for awhile. I bought it with the idea of starting a rodent colony but went back on my plans. I decided not to waste the Hay and I've been using it with my snakes until the bag runs out. They seem to like burrowing in it. I probably won't buy another bag though, I'm unsure if the Hay will cause dust and respiration problems after long term use.
I hope that helped! I prefer the look of aspen to the compressed wood, but at this point price has me won over the aspen!