So, unfortunately I think you're going to have to start small for $500.
To set yourself up for future expansion, you'll want to run 6/4 so that you can handle a 50 amp service. Not sure how far your run is but I spent almost $200 in 6/4 alone.
Also, aside from the larger kettles and wire, you're going to need:
- a NEMA enclosure ($100)
- a spa panel or GFCI breaker ($100+)
- BCS-460 ($200)
- PID, SSR, other components, wiring ($100+)
- Heating Element, some sort of element housing, etc ($50-150)
- ventilation ($100+)
All said and done, you'll be looking at almost $1000-1500 with the kettle added in. A lot of folks may spend twice that.
Personally, if I were on a limited budget, I'd get the 220V 50amp run done, get your larger kettle, and go with a simple DIY controller like this:
That should be able to get you to your $500 budget and allow you to expand easily in the future with minimal loss in not-so-useful equipment.