I think you have just made your decision - if you want VHF & UHF multimode (i.e. SSB and CW as well as FM (and AM)) then the Yaesu FT-817ND/818 comes with all of that. You would have the option of adding a 2m transverter into the Elecraft KX3 and I’m sure that overall the receive performance of the Elecraft over the Yaesu would be better on HF & VHF - but for a price. Do you really want an expensive rig thrown into a back-pack and carried in all weather up hills?
Remember that once you get away from metro noise, all rigs perform a whole lot better than from your home QTH.
The second hand FT-817ND at $300 sounds like the best option (IMHO). If you bought it now, you could use it on 2m & 70cm before you get your general licence and listen around on HF as well.