This is the property in question. I'm not going to bid on this specific property, but wanted to get feedback on how to evaluate capex costs for a property with no access to interior. Back of the napkin math:

Nearby fourplexes selling for around $200k. Rental income somewhere around $650 x 4 = $2600 / month. Pretty solid cashflow. Now the big elephant in the room is that the listing price is $76,960, BUT there's no access to interior. So how am I supposed to figure out what the cost would be to get the property in rentable shape? Anyone with experience in rehabbing foreclosures have a ballpark estimate?

Ask yourself, why is there no interior access? Is it because there are tenants in place? Is it because there is a safety issue with the property making it a hazard to enter? Etc. Based on the listing, the city blocked access. You can assume it is vacant and not safe to enter based on that. Additionally, if it was a tenant issue, you can make interior access part of your due diligence contingencies. If the owner really wants to sell it, they will make access happen.

You need to find out why the city locked it up, @Edward Yu . This should be public record. That's something to start with.