this reminds me of an old football story:
some years ago, there was a partying veteran, who liked to hit town the open day after each game (normally tuesday), and he invited a rookie to come along one time. they had a great evening, hit several bars and dance clubs, and the rookie kept rough mental track of all the money the veteran spent during the night.
the next day, the rookie asked the veteran about his profligate spending for one night of fun. the veteran said, "hell son, i made $500 last night!" "what? you spent at least $1000 last night, how did you make $500?" "well, i had $1500 worth of fun, and it cost me $1000, so i figure i made $500!"
as for the direct costs of this little project? i don't know. bought some lumber, magnets, a hinge, some plastic-dip (black, all that was available), and some green felt, and glass, already had the plywood bottom material, stain, and poly.
but i enjoy the challenge of such projects, and when it is done, someone else will get to enjoy the results, so that's good news.
