i've not downloaded it just yet, but i have an idea you could use: a scoreboard-based "shop" system. you'd need 13 command blocks, one for each item and they basically say "if *item* is on the ground near the player, increase scoreboard by *item's worth* " and then you could throw down 1 glowstone dust to open the interface.
the interface is a chat-based click menu, each item on the menu would serve two purposes: firstly it would reduce the scoreboard by the value chosen, and secondly it would give you that thing.
additional idea: if the score goes negative, it will give you blindness, slowness, mining fatigue, weakness and so on until you've returned it to 0 or higher. and if you don't mind an extra two commands, you can make it worse every 20 below 0, finishing with level III debuffs at -60 and lower.
to make things easier (and not make several full one-commands), i'd leave it at the minerals. maybe include cobble as 0.01 also maybe make iron 16, redstone dust 2 instead of redstone block 2, lapis dust 2 instead of lapis block 18.
so in summary, if you were to accept all of my ideas, i reckon it would fit into two one-commands made with McEdit.