You didn’t mention if you have any other snakes that may have been exposed to the mites. If so, then Ivomec (ivermectin) as an injectable would be even less cost effective. Even if you need to treat only that one Burmese, you will still have to clean and treat its cage and any cage furnishings, preferably more than once. So as long as you have two cans of Provent-a-mite on the way, take my word for it - if you follow the recommended procedure, you WILL get rid of those mites!
Some people use ivermectin as a topical application for killing mites. If you check in with the Herp Health Forum and ask for Oldherper, he can tell you how he goes about diluting it for spray use and perhaps where to buy it. I’d advise caution in the “if a little bit is good, more is better” school of mite treatment, however. Unless you’re using something like water or vegetable oil for treatment, all of the effective treatments for mites involve “poisoning” these critters. Piling on different kinds of chemicals in rapid succession might produce toxic results for your snake. Just another way of asking you to give that Provent-a-mite a chance. 
One last warning since you didn’t mention what other herps you have: Ivermectin should NEVER be used in turtles or tortoises.
If you (or anyone else reading this) care to email me by clicking on my username above, I’ll be happy to send you an informative paper on recommended – as well as non-recommended – treatments for snake mites and ticks.
Good success,
Joan