So, I have now successfully taken a 200 dollar cello and tuned it to standard E1 bass tuning - using DAddario jazz flatwound guitar strings.
No, it does not have lots of volume. Neither do many acoustic basses.

But, it has very good, quiet tone, while giving me stable tuning at E1.
This is on a 3/4, so we are talking 23" scale guitar scale bass - mini double bass.
Next step is a decent pickup, but I will need to wait on that. [post retirement - discretionary spending no longer a given.

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If it goes well after the pickup, I will probably create a separate thread just for specifics of the parts, in case anyone wants to kick the tires.