i dont know how game maker stores its data since it seems to be a "dynamically typed" language. but lets assume the worse and say if for some horrible reason everything is stored as a string then it would take (assuming a character is 1 byte, counting only the key and value strings, and not worrying about null-terminating the strings):
[price] = 150 (8B)
[description] = a big nusty (22B)
[stat1] = 6999 (9B)
[stat2] = 7000 (9B)
theres 8 + 22 + 9 + 9 =48bytes. if you had 1000 of these item definitions you would have 48000bytes or 48KB, aka not shit nowadays. textures on the other hand use
(width * height * components[rgb=3 or rgba=4] * subimages) bytes
the main character sprite for cr*z'd is
32 * 32 * 4(idk if gm7 stored all textures in rgba, u could load files with nonbinary alpha transparency in with it so im going to say yes) * 64
= ~262KB. which is still not a huge deal (i think average ram is at least 4GB nowadays) but obviously more significant than a bunch of data.
in general, you neednt worry about storing data, you have plenty of room to play with that. make wise performance choices instead