You could go to Target and get the adjustable metel shelves ($49) and put your tubs on those with the heat tape under your tubs. They are not very expensive and neither is the heat tape. Thermostates are more $$$. And each shelving unit should have their own. Then you could cool the adults for breeding and keep the babies at a higher temp. And you are probably going to have to heat the entire room anyhow even with heat tape. Most houses are set to 72 or 74, right?
And these racks (shelves) are no tools required!!!