This past Christmas, my daughter asked for, and received, a Slurpee Maker. We found it at KB Toys for $18.97. Although it's not made by 7-11, and doesn't even have their logo, it's advertised as making "real 7-11 Slurpees".
She thought that it would be fun to make her own, and I thought it would be more convenient by saving alot of trips to 7-11. We both couldn't have been more wrong.
She put in alot of time, effort and trouble for every tiny half-melted/half-icy concoction. (I refuse to call it an actual 'Slurpee"). The first time or two were fun for her, but then the novelty wore off when she realized all of the work and time that was needed, and how dissapointing the actual result was. She had to add crushed ice, salt, warm water, and juice or pop. Then, she had to turn it on for 5-10 minutes. It's extremely loud, like a cheap blender. Perhaps it would work better if it had an electric motor, which would be more powerful, and quicker, than the battery-operated one in this. (4 - "C" batteries, not included). The result is a tiny cup of loose, watery "pop"(?) This is a terrible, terrible product. Neither fun, nor makes a quality Slurpee. It's rated for ages 8 - 12, but I don't think kids of any age, younger, or even older than that, would be happy with this machine.
Instead, just give them the $20, and let them use it on a summer's worth of trips to 7-11 to get the real thing!