Reddit mentions of 500 FT (500FT) Bulk Fiber Optic Cable Multimode 50/125 Duplex (ON Spool) 150M

If "best" means "fastest and highest quality", using 2 fiber transceivers and running fiber via conduit to the guest house would definitely be the best way. OP's definition of "best" may be different, though.

A more sensible approach would be to use 2 directional wireless antennae pointed at each other. You could even mount the wireless antennae in stainless steel salad bowls to increase the reception. It sounds like a joke, but it's not.

> Fiber cable is really expensive

Untrue, it's not the cable, it's the connectors and work to install/terminate it. Raw fiber is relatively cheap. it's about 2x the price of copper ethernet cable if you buy in small quantities.

> you can't splice it or cut it into custom lengths like Ethernet

Untrue, with multimode you certainly can cut it to length and terminate it by hand. It's a pain in the ass, and requires some specific hand tools, but doable. You can hand 'splice' 2 pieces together by terminating both ends and putting them in a coupler, but it's not recommended due to signal loss.

If you just want to buy working cables off the shelf, yes, shielded cat6 works fine, but fiber isn't this magical unworkable monster. Single mode requires specialized tools to terminate and splice, but multimode was made to be easier to work with by hand, while still giving better distance performance than copper.