@Carly M. Estimates are supposed to be reasonable guesses, but a good PM's estimates shouldn't be that far off. The estimates from my PM are always spot on, and if they're off by more than a few dollars (only because there were additional problems found), then she sends me another message for approval before starting the work.
When I redid my own yard, I don't think I even spent 3k for a FULL overhaul including 2 dozen roses, 2 dozen shrubs, a small patch of lawn, several creeping vines, a completely new irrigation system, path lights, spotlights, removing about 4 ton of decorative rock and replacing it with another 6 ton of rock and river stones for my front and back yard (desert landscaping), along with the usual trimming and pruning.
Of course, I'm sure that KC has larger lots than Vegas but you're just cleaning up. That shouldn't cost very much.
Oh yes... and fire the PM regardless and check with an attorney. This is purely for the fact that the PM felt it was just fine to approve work for 3x the original quote without talking to your first. OR because the PM picked a company that would rip you off for 3x. OR for allowing this to happen. OR... you get the picture. Whether he is trying to rip you off or just utterly incompetent, your PM has no value... actually he has negative value. My PM's value is in the money she SAVES me when something goes wrong, not just in managing my affairs. I almost never pay more that what she says it will be, it is almost always considerably LESS that what I can get quoted myself. Case in point, my friend was quoted about 3k to repair her AC unit. She's not very well off, so as a favor, I asked my PM to send her AC person over for a quote which ended up $1700 (condenser). I should mention that the first few years, I did get my own quotes on the side for any work she said needed to be done and I still get my own quotes on major work for comparison's sake.