I currently own and KX3 and have owned an 817ND with an Inrad CW filter. After purchasing the KX3 two years ago, the 817 became "dusty".
Let me say up front that the 817 is a good radio. It is sort of a "shack in a box" in that it does everything 160 - 440 all mode. That said, the receiver in the KX3 is significantly better (and quieter) than the 817. Also, since the KX3 is an SDR, every time there is a software update, you essentially get a new radio.
The 817 is "old" technology. The rig is over 10 years old and honestly I'm amazed that Yeasu has not replaced it with something else.
The KX3 does cost more. If cost is an issue, then you need to decide what you can afford. You can build the KX3, which is not difficult. It is just a bolt together kit. No soldering. That will save you $$$ and could allow you to afford an extra option or two depending on what you think you need. I choose to add the tuner (which will tune a wet noodle), the roofing filter and the batter charger/clock option. Later you can add the amp and have an awesome 100 watt station. Again you need to decide what you can afford, but I subscribe to the "buy once, cry once" theory.
Waiting for Dayton to save a few $$$ or get something extra may not pay off for a KX3. In the past, Elecraft has offered free shipping. They don't bring products to sell, they just take orders. So if saving a few dollars in shipping is not a big deal and you choose a KX3, then order now.
Full disclosure, I am a Koolaid drinking Elecraft guy. I own both the KX3 and built a K3 and P3 in late December.
Welcome back to the hobby! I am sure what ever you decide, you will have a great time.
Mike - KI8R