^redacted‌--Thanks so much for the tag. Tom--There are so many valuable comments above. I'm happy to chat if helpful. I would start by checking CBRE & Cushman market reports for the area to get a rough sense for market rents by tier. Actual lease rates for your building versus the others will depend on how it's features compare with those of the broader market, operating expenses, tenant improvement allowances, and lease terms. As noted above, you would be well served to connect with a tenant rep and an investment sales broker who can opine on rents and asset values respectively. You definitely don't need an appraisal. You may be hard pressed to get a broker to provide a formal BOV when you aren't offering a possible listing.

Estimate market rent by triangulating. Ignore the seller's “normalized” rent. Start with 8–10% of property value, confirm with $/SF comps, ensure rent stays within 4–10% of revenue, account for NNN vs gross, and model 2–3% annual increases. Use the higher of asset-based rent or comp midpoint, then stress-test ±10%.