Check craigslist like Price mentioned. Because they are on there all the time from $500 - $1500.
All of the reviews I have read about the new hoss say they are not impressed with how it wrks on low flow. They all seem to point to using the high flow version. So I think the RX-20 would be the better way to go. Also like Price said. Others are using it with similar set ups to yours and are very happy.
If I had a powerful enough portable to be able to run it from a van or trailer I would certainly get a
propane heater before I put money into a rotary extractor. I have used RX20s and they can be great
tools. Even with my White Magic(1990s)which normally would provide with a wand over 200 degrees
cleaning solution I had to add a 2HT inline when using a RX20. With the setup as I described I was able
to undo the damage done by bonnet cleaners( supposedly carbonated) used previously for 2 years on a carpet
at a skating rink.
With the solution tempatures over 200 degrees with high flow with my RX20 I must have used 200 gallons of cleaning solution ,very hot cleaning solution I watched almost black syrup come out of that carpet. Eventually it
cleaned up. The point is I had a lot of heat ,tremendous vacuum ,high flow and rotary extraction to get the
ground in soil out of that carpet.
So can one use a RX20 with an electric powered portable/ truckmount? I think so but you must have heat and likely
along with for instance electric Portable /Truckmounts you may need a power booster to have acceptable drying times.
Also would jet down somewhat .
Seems like the Roto Vacs are better suited for ETMs or Portable /Truckmounts as they have less flow. May take longer
but perhaps having more control over how much solution one is using is better than not really knowing how much
solution you are using. RX 20s are better suited for gas powered truckmounts in my opinion.