Have you tried FireAlpaca? It's less powerful than Photoshop, but it has some great points-- it makes sharp lines, has a stabilizer like Sai, and includes a simple perspective tool that's really effective once you understand how to use it.
You shouldn't mention cracks and other illegal methods on here, I think it's possible to get banned for that. :c
OP, I prefer SAI as well, so it's worth it to get the free trial. If you like it, it's much cheaper than Photoshop. If not, hey, a free month to try still doesn't hurt.
GIMP is also a decent option, though in my experience it can run a little slow and doesn't have the best interface.
I would recommend Paint Tool Sai, it's cheap and widely used. GIMP is okay but I hear it has problems with tablet sensitivity, and I personally hate the interface... A really neat free drawing program is MyPaint. It is limited and you will need to crop your images in another program (even just Paint will do fine) but it has a large selection of brushes and provides you with infinite drawing space. C:
Sai has a 30 day free trial and you can find cracks easily.
SAI has a better quality and you can change the level of your brush strength...
if you want a real good idea on all these programs, go on youtube and type them in, you can watch how other people use them.emotion_yatta