Any question answered...

The hub on my Haro Mary SS seems shot. 50% of the time pedalling works and the pawls engage. The rest the freehub just spins freely in both directions.

I know absolutely nothing about single speed hubs using short freehub style bodies. Is there a cheap solution out there? A Novatech or similar go to hub that's a default choice for replacement? Could get a regular fixed disc hub and run a freewheel without chainline issues? Any benefits to a particular solution (other than that I already have 2 or three cassette style cogs)? Should I just post a wanted ad on singletrack world for a whole wheel? Should I see it as a sign to stick a mech hanger on it and shift to 1x9?

I had this bike and am still using the rear wheel from it on my current bike. I've been looking for a similar hub for when the current one dies, haven't found anything else like it. Just want another MTB hub with enough room for just a single sprocket.

A fixed disc hub with a freewheel would work fine, only downside is if you want to run different ratios alternative freewheels are a lot more expensive than alternative sprockets.