My GPA now overall is a 3.24 (maybe a 3.3 upon graduation). If I do an informal post-bacc, retake those 4 classes and make a minimum of an A- for each, my overall GPA with the grade-replacement policy would be a 3.53 overall. This is also assuming I make an A- or better in the biochem class I am retaking currently this semester before I graduated.

Or should I shell out 20k$ for a post-bacc taking upper level classes? My trend has been increasing the last few semesters. I've made a 3.8 and a 3.775 my last two semesters. It's just those chemistry classes bringing the GPA down :( and my MCAT score won't come back for another few weeks. What do you all think?

retake. for DO, no sense in shelling out $20k if you don't have to.

Strongly concur with this poster. You're in the ballpark of being competetive for a good number of schools, ans the re-takes will be fine to get you interviews pretty much at any DO school.
good luck!

retake. for DO, no sense in shelling out $20k if you don't have to.

What about taking 2 classes, and up with a 3.45?

If they're pre-reqs, you should probably get A's in them if you have a C or worse.