You can figure about 10lbs a Gallon. So about 1250 lbs. That's a lot of wieght. You might check where you plan to put it, which way the beams in the floor run. You want it to hit across the beams. IMO I would reinforce the floor from underneath. I played it safe.
As far as RO cost, I got it for our 125 and it was about 3.50 for a 5 gallon jug. You had to return the jugs after.
terry