That looks pretty folder specific given it's 58T. Depending on what tooth size you're after, 104mm might be difficult to find as the cheapos only go up to 38.
It says "BMX Folding bike" in the title (of course they just put whatever the hell in the title) but looks like you're right, the 42t 104BCD ones are £15. I'll just get that J&L then. Thanks
Ah, thanks, I didn't try eBay. The AliExpress ones are all weird things like this one, I assumed eBay would be the same