I took one class (computer architecture & assembly language) through Oregon State University's online CS program as a soft-requirement for some in-person classes I'm currently taking. They have the full post-bacc program (http://eecs.oregonstate.edu/academic/online-cs-postbacc), and they also do allow you to take one-off classes. Officially it says you can only take the intro classes, but I just signed up for this class anyways.

It was quite a bit more than OP's budget (total cost came to $1,200 or so), but that ended up being much cheaper than having to take the class at my current program. My employer also helped with 2/3 of the cost.