I met the bank appraiser during his visit, and he shook his head at my purchase price in amazement.A year later, a duplex, now valued at $240K was advertised in the papers for $180K, also by an agent.

As mentioned in a previous comment, you don't want a cheap appraisal/inspection.

Current Mortgage: $75k, Appraised at $160k 4 months ago.

Purchase price: $115,000 Cash invested: $60,000 Sale price: $235,000 2/1 Single-Family Investment PropertyLocated in an area primed for revitalization, I purchased this 1915 home for $120k, with an “as-is” appraisal of $186k.

Not only does the buyer still have to pay full price, appraisal fees, inspection fees, etc. now they have to pay their own broker. 

They are claiming the house I'm looking to buy should rent for over $200 what I'm finding on rentometer, craigslist, zillow, etc, and even a rental appraisal from my house's appraisal report. 

Search the BP for ADU appraisals to encounter numerous examples.

If I'm able to make a cash purchase, do you recommend stabilizing the property before seeking a DSCR loan i.e. is it better to use a DCR based on real rental income once the property is leased or based on a rent appraiser before leasing?

If so, are there any RE professionals on BP who can help me out with the land appraisal comps?

The last thing you want to do is shop it yourself, have no clue on the bank's closing rate, and guidelines, and pay for an expensive appraisal with no loan.