Phenidone has been proposed by Jay DeFehr at Flickr in a concentrate to be used diluted as one shot developer. Following this line, I made, just for fun, the following cheap developer:
0,5 g/l Potassium Metabisulfite
10 g/l coffee
5 g/l Vitamine C
0,2 g/l Phenidone
20 g/l Sodium Carbonate, anhydrous
I used it as is and developed a film for 15 minutes the first time. I kept the solution to see if it could be reused. Yes, next day it worked again in the same time. Three days after, again, two weeks after, the same. I forgot at the shelf the clear glass bottle where I stored the developer and, two months later, I just tried to see if it was still active and it was, no changes in developing time. Now, some 4 months are gone and yesterday I developed again and it worked like for the first time. I used 20 minutes just in case but the film has been a little overdeveloped. Until now I have developed 12 rolls with this developer, no visible changes in activity.
Disadvantages are (using 1991 expired TMax 400) the huge grain and some fog. Maybe adding about 0,5 g/l of Potassium Bromide will solve fog problem and improve graininess. Alkali should also be increased to keep the same developing time, I think.
P.S. I made following changes to the developer: add 2 g/l of Sodium Carbonate and 0.5 g/l of Potassium Bromide. One of the pictures of the last developed film: