I feel like we have known each other for a while, so please allow me to be frank.
BullCrap. Times are too tight to worry about him. If you honestly think it would be worth your hard earned money.... and you are willing to spend more of your hard earned money to "fix" it then go for it. If it isn't then DO NOT DO IT. Shelves right now in the hardware stores are VERY inexpensive. You can make a rack full of tanks with less money... and they are CLEANABLE!!!!
If nothing else, make it interesting. Regardless of whether you plan to buy it or not... tell him you really like the rack, but after doing your bills tonight you realized that you just can't do it.... the most you could possibly come up with right now is $50 cash.... and you know that isn't enough..... and that your very sorry.....
Then be absolutely quiet for a minute... and see what he says. I don't care how uncomfortable the silence is. just be quiet... and let him speak...
Negotiations 101.
Thank me tommorow.