My RO uses 2.5 x 20" filters, I get them at $3.00 each by the case thru Ray Gingerich. I've never been able to beat his price. However I finally found them on Amazon at essentially the same price ($74.95/25). In the past prices were between $4.50 and about $20 each for the same filter. I like the blown poly filters far better than the string wound type.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.