@Brian Green the $7,500 you see is an excel spreadsheet number or a lazy guesstimate from the property managers renovation super. Your numbers are about right except the biggest corner cut is flooring. An inexperienced owner will fall for the rolled laminate flooring trap. Cheap rolled laminate can be installed for as little as .50-.75/sq foot labor and materials. They use the stuff that looks like real plank/tile/wood and in the pictures it can look decent. Problem is that it is as bad as carpet and lasts 1-2 turns. First piece of furniture or appliance moved in will gash this flooring or just one water leak and its difficult to impossible to replace so it is being turned VERY frequently and the front end savings are offset over 3 years with replacements.
Another consideration is size of a unit a 500-600 sq foot unit can probably be turned for $7500:
Appliances:$1500 - I'm getting sets in bulk under $1000 but you have to know how to do this and you need storage. Your PM won't be of much help here. PM likes to order from one of the big delivery companies HD or MD Supply at 5-20% above retail or a "deal" that they have with a company like GE. Shop around, this is one line item where you can make a big dent in the budget.
Rolled Flooring: $500 - Not recommended but being used. Most skimp on replacing baseboards but that is a must with any new flooring other than carpet.
Quartz Countertops: $1000 -
Paint $750 - if your turning a lot of units it should cost less than $1/sq foot and doesn't include scraping popcorn ceiling. $1200 if scraping popcorn.
Cabinets $1200-1500 - Can find them for less than $1000 bulk negotiated
Light fixtures and electrical - $700
Plumbing fixtures - $900
Shower surround - $1000
And there you go $7,500 or less. Keep in mind none of this includes the dry rot remediation, subfloor repairs, etc. You find a lot of problems in a 40 year old building once you begin. YMMV depending on region. In the Bay Area for example people are paying $2-3/foot for paint and $4-10/sq foot to lay the right flooring. The big shortcut to get to budget is using rolled laminate garbage and this is an enormous mistake because when all the units are done and repositioned for sale the next buyer will walk the units and they will look like the flooring you had in the unit before the remodel. Problem is that using laminate plank (also not a fan) or tile destroys this budget. But sounds like your thinking of doing this the right way.
Finally when a broker tells you "$3500/door" just ask that broker how many apartments he has turned.
Here are a few pics of how my units look and I can't touch $7,500. I've been coming in at $9-11k and that has not been easy.