Ellis, are you sure that they are spider mites? Tell us what you've seen with magnification. How did you identify them?
Whatever the pest, Neem Oil is a natural horticultural oil that may work, but it takes a regular spraying program. The oil has to touch the pest to kill it, and it may not kill the eggs. So soon after spraying, when more eggs hatch, the pests need to be sprayed again.
Don't Bug Me and other natural pesticides made with pyrethrins, are the next step. The natural pesticide is toxic, but breaks down very quickly.
Avid and other miticides are a much more powerful pesticide, that also is an ovacide (kills the eggs). Some shops sell a small eye-dropper bottle for 25 bucks or so. Like was said, only a few drops is all you need. This shit is way toxic, and you need to wear protective gear when spraying.
HTH