I agree, usable replacement ought to be cheap, there's nothing special about those transmisisons.
That said and as crenwelge mentions if it's better than average, close to home, and so on you could be money ahead even if you end up paying more up front. lots of factors to consider.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-