I ordered a new one off of Amazon this year.
https://www.amazon.com/gp/product/B00AXT5H4M/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
If you are using a waterbed heater you'll need to use a vinyl liner. What were you planning on for this?
My benchmark for comparison of the equipment performance are the Samadhi-Eco (~$7k) and Zen Tent (~$2k) performance, since these are the most likely candidates for a residential purchase.
Heater:
Samadhi rates the performance of their heating system to “within 1/3 of a degree”. I couldn’t find an accuracy rating for the Zen Tent. A quick internet search pulled up this waterbed heater:
https://www.amazon.com/InnoMax-Thermal-Guardian-Quantum-Waterbed/dp/B00AXT5H4M/ref=as_at/
This is a solid state computer controlled heater accurate to within 1/8 of a degree from the set point. One of the cons here is that it uses an analog dial as opposed to a digital LED read out (like the Zen Tent). Amazon sells this heater for $54.95. Solid State waterbed heaters such as this one (a single heater per tank) were what was used in the early commercial tanks of the 70s and 80s) I used them in my two builds and they were quite satisfactory.
Filtration:
Filters only take out particulate (skin, hair and other small debris that builds up in the tank). They do not disinfect the water.
u/JettaGLi16v (he's a pool and spa guy and knows his stuff) recommended this pump/filter combo:
https://www.amazon.com/Intex-1000-Gallon-Filter-Pump-120-Volt/dp/B005QIYL7E/ref=sr_1_5?
This pump/filter combo is rated to an actual gallons per hour (GPH) of 750 (the pump is rated to 1000GPH, Zen’s new system pump is rated to 1700GPH). A tank that is 4 x 8 by 12” of water is approx 250 gallons. This gives an effective turn over of 3 times per hour of filtration. This is more than sufficient for the average residential user. Amazon sells this item for $35.99 This pump/filter combo lacks the UV disinfectant of the Zen Tent. u/JettaGLi16v has real world experience with this pump installed in a tank that he built a number of years ago. He has some great recommendations for maintenance. As far as the UV lamp is concerned I'm not sure about how that works. Again u/JettaGLi16v might have more info here.