Elecrafts are sweet radios. Haven't seen the KX3 up close, but the K3 is uber nice. One of the best receivers out there of any radio. Sherwood measured the KX3 above the very awesome FTdx-5000 and higher than the K3 itself. It's only second to the PT-800, which is undisputed king of the hill.
Base KX3 is $900 if you assemble it yourself. Also does not do VHF or UHF. But compared to a FT-817, it's not bad. Those go for about $700 new right now and there's no question the KX3 is a much better radio. I have an '817 and do like it a lot. I think the form factor is better than the KX3 and it had a unique niche unto itself for a decade. But it's performance is that of a design badly showing its age.
The regular K3 can accept a 2m module. But to get a K3/100 starts at $2100 if you assemble and the 2m module, which is 10W, is $300. If you want to do UHF you'll need to add the transverter module to the 2m module to drive a UHF amp.
For around twice what the 2m module alone costs you can get a whole FT-857, which you can find right now at around $850 brand new. That's another reason the FT-857 is I think the best choice for a first radio. You can build a battery pack for $50 and have /way/ more radio than the $200 difference to the '817.
But of course the radios we mortals can afford are straight up lousy in comparison. The FT-817 3rd order dynamic range comes in around 83dB and the ft-857 at about 88dB/65dB. Those are around 20dB worse than the K3 class radios.