My favorite treatment for mites, comes from Walmart as well...
Go to the section in the store where they sell human lice treatment...
You are looking for 'Equate' brand "bedding spray for lice"...it's a small aresol can, and the only active ingredient is 0.5% permethrin...runs about $4...
Remove the snake, substrate, etc...put the old substrate in a garbage bag and get it completely out of the building as quickly as possible...
Clean the cage thouroughly with a mild bleach solution, mites are filthy pests...this will not kill the mites/eggs, but will eliminate any bacteria or viruses they may have smeared around...rinse it out and let it dry really well...
Do the next step in a well ventilated area...outside if possible...evenly spray all over the cage...inside, outside, bottom, lid...(this will help kill stragglers that might crawl out of the cage, air holes, etc...
Also, whatever new substrate you are going to use, spray it as well...I reccomend white paper towels...this makes the dead mites much easier to see...and gives them no place to hide/lay eggs.
Let it dry completely, I leave it for at least 10 hours...the spray is safe if dry, but it
must be dry...the propellant is harmful if inhaled, and needs to evaporate completely...
Once this is done, place the snake, substrate, water, back in the cage...the mites will die on contact with the permethrin when they fall off the snake after feeding...the spray has an ongoing effect, it keeps killing the mites for weeks...eventually there will be none left...
I usually repeat this treatment every two weeks, untill I haven't seen any dead mites in the waterbowl or cage for quite some time...
Hope this helps and good luck...