I don't know it was a lot smaller than a lot of them from back East, Fort Griffin from its 1864 blueprint was no where near the size of other forts.
One of the things that probably contributed to its smaller size is that unlike most Earthen forts they didn't build it up for elevation, Fort Derussy in Marksville, LA had its walls built up to twenty feet above ground level, Fort Griffin wasn't built up hardly any above ground level, thinking back I'm not even sure it had a glacis for stalling an infantry attack. Fort Griffin's design lends itself more to a redoubt built solely for fighting off the type of attack it repelled during Sabine Pass, if the naval squadron had dropped off their infantry at the shoreline and they attacked the Fort, it wouldn't have been able to fight them off as its design is almost entirely artillery oriented and doesn't lend itself to defending against infantry.
Compared to other forts, even Fort Magruder in Galveston, Fort Griffin is more redoubt than fort, and it would be an easier proposition to rebuild cost wise, (especially if it were a more private affair, contractors get greedy when governments are making the effort), than rebuilding many other forts, as Fort Griffin was more a redoubt and a lot smaller than its contemporaries. But I could be wrong on the costs, other forts usually have the original ground to build on, Fort Griffin's ground is gone, the most cost effective way would be to direct an effort of all excess dirt being dug from a 100 mile radius be dumped there instead of normal dumping grounds.