I started off with two lengths of scrap 2x4 each measuring 11" long on the table saw.
I then drilled a 1/4" hole through each pair, and inserted a T-nut in the lower of each
These then slot through the top half of the sanding block, into the T-nut below, once you have your sandpaper in place, they are tightened, and your sandpaper is going nowhere until you want to change it.
I now have four sanding blocks, one with a shaped end for getting into tight corners. I can either put in different grit in each, or load them up with the same grit if I have a big project, such as the dining table and chairs, that way I am not wasting time changing sandpaper. The final dimensions of the blocks are 5 1/2" long, by 2 1/2" wide by 1 3/8" deep.
The only addition to this may be that in the future when I have my router out for a bigger job, I may put a roundover on the tops to make them more comfortable in my hand, but they work, and I should have done this before starting the dining room suite.
This project cost me nothing as it was made from scrap and hardware I had in stock!