I have also had a "little" problem with spider mites, but i used this:
4 parts water
1 part liquid brown soap
1 part Alcohol (not the kind you drink)
used it 3 times with 3 days apart, and then the problem was solved,
use a lot of the stuff, also remember to get the underside of the leafs.
The best is that it works, and it's a lot cheaper than $200

If you want to use biology, you can use "Phytoseiulus persimilis", it is a mite
that eats spider mites, but that solution is a bit more expensive.
Good luck.