For the aggravation of the conversion if you did it yourself, money spent doing it yourself OR hiring it out and resale potential, I would not change the transmission. I'd sell the car and buy a manual transmission car of similar size.
Go to fueleconomy(dot)gov and see what the car you're looking at is rated before you buy. Many cars there also have been rated by {presumably} owners so you see what others claim the vehicle really gets. As you're getting a manual transmission versus selling an automatic transmission, if all else is equal, you should have less money tied up in the car after the exchange. Of course, that depends on a private sale and private purchase. Dealers margins would change the situation dramatically as would buying a "better" car than the one you have.
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