Do you mind If I ask what you Consider a reason able price?
Watch this Video on Installation of the Flat Rock Sheets. Basically all product are the same when it comes to Cutting.
YouTube - Universal Rocks - Rocky background in all sizes!.wmv
I am Assuming that there would be a few Inches of Substrate at least I See that the Flat Rock Sheets have several That could cut down to accommodate widths of 16 inches
How many Tanks do you Have? Are You want to do just the Backs or also the Sides?
They Make a 48 x 28 sheet that could do 3 Sides or 3 Backs only. Which At a Typical Mark Up in a Business Would go for less than $80 US. If you cut it Down to 3 pieces that would be less than $28 US per Background.
Is that InExpensive Enough?