It's on a square footage basis. CBRE publishes semi annual market updates which also includes retail. As a general, can estimate based on that. But of course there will be premiums for certain locations. Also, adding to the complexity are other costs to be negotiated. My friend, recently took over a franchise in the PATH that is run by Cadillac Fairview, and said that they got you by the ballochs. They have it all figured out so you'd better have the money ready and willing to handover.
Also, rarely do you just get into a lease negotiation with the owner of the property. You buy the rights from the existing lease owner which could be hundreds of thousands. This of course could be recouped when you sell, but that value can also vary too. Also, the mall owner has significant say and restrictions on what type of business is operated. You can't just change it.
I helped my friend to paint something (small section of a wall bc it was dirty), but he even said don't let anybody see you as you're supposed to hire the unionized workers. Crazy how there are all these conditions and restrictions. But hey, you get guaranteed foot traffic.