You really don't need anything huge for a 2.5 car. I'd look into something like this Logitech Bluetooth receiver:
http://www.amazon.com/Logitech-980-0...tech+bluetooth That way, you can use your phone or tablet to play music on anything with a stereo input. I'm still browsing for accompanying gear and staying under your budget.
EDIT: Here we go, amp and speakers, too:
http://www.amazon.com/gp/product/B00...A385A0XNQBW8HY Those B652 speakers are one of the best at their price point, and that amp should be plenty enough for your garage. You can buy it all on Amazon and it'll run you a hair under $125 shipped. Best part is, that amp can be powered by AA batteries, too. You can take it camping or put it in a car trailer when you go on trips. Dual purpose :)