First you have to kill the mold - just cleaning it just moves the spores into the air where you can breathe them more easily but doesn't solve the problem.
A strong UV-C light will kill many types of mold, but not all. Strong UV-C light will also burn your skin and retinas, so not to be fooled with lightly.
The lady quoting $600 was actually probably not far off - remember she said "proper" and if that's one of the more aggressive and dangerous types of mold "proper" cleaning - that completely removes the mold permanently without just moving the spores around - can be quite expensive.
In Texas and Louisiana (and I'm sure other places) very nice houses have been condemned because of mold in one or two rooms.
Oh, ozone can also kill mold, though less reliably than UV-C and the ozone has to be strong enough to be uncomfortable (and probably unsafe) to breathe. There is some evidence that the simple ozone generators that some people have in their homes do help prevent mold from growing - but if you already have mold they probably won't kill it. For that you have to bring in the heavy equipment.
John