^agree, but get a zee mech in short cage the one that can handle a 36t. Unless you already have the parts 10spd beats 9 in performance and is only slightly more expensive.
To answer the OPs question, the cheapest option is what Blakey initially suggests (to lock out the FD); otherwise bashring and N-Gear Jumpstop, or do away with the bashring and run a MRP 1x (upper guide only), or a Paul chainguide. The MRP is better.
If you’re riding really fast rocky trails you’ll still get your chain bouncing off very occasionally (esp, if you backpedal). You can run a Bionicon C-Guide if that proves to be an issue.
10 speed clutched is better but the above options work too.
If budget is the objective, i made a pretty good facsimile of an MRP top guide out of some nylon stock and alloy. saw/file/drill/tap is all that’s needed. sold with bike so can’t get a photo of it.
Worked better than my pauls guide does on 1 x 9.
If the OP already has sram 9sp shifter and some 9sp cassettes/chains, then I stand by my shimano 10sp clutched (deore RD-M615 for max budgetary) plus sram 9sp shifter. (maybe plus 5mm cable clamp spacer, appears to work without it.)
If not, then definitely do: 10sp Saint shifter, Deore RD-M615 clutched mech, locked out front mech, cheapest available n/w ring.
Update:
Have a 73mm bb and my bike is a 63mm shell.
The chain ring hit on the frame so I swapped the spacers to the drive train side.
But now when in 1st n 2nd the the chain line is too wild and pulls the chain off under load… and this was just on the work stand!
So ill have to rethink this!
Im also keen to make my own chain guide from an front old derailer!