Q: how much would it cost for four new speakers and maybe an amp and a new radio?
A: speakers look at spending atleast 50-100 dollars per pair for a decent pair of speakers. so I'll just say for 4 speakers around 150
A radio - expect to spend about 100 bucks
amp - if you want a 4 channel amp for your speakers, then expect to spend atleast 200 dollars for a decent one.
Q: and installation? where would i get this done?
A: installation costs varies. it is heavily dependent on what you want to have installed, what you will need to buy to have it installed, and who installs it. installs can get pretty pricey. because you'll have to pay for labor, and all the wiring and other parts needed to install your equipment.
best buy charges 50 dollars to install your new radio
100 dollars to install an amp
and 40 dollars to install one pair of speakers.
plus with that amp install you'll need to buy an amp wiring kit, and for the stereo install you'll need a wire harness, and possibly an antannae adapter.
Also if you want your system to bump, then you'll need a subwoofer, an amp to power that subwoofer, and a box for the subwoofer.
all in all you're looking at quite a bit of money if you have all of this installed for you. I would focus on getting one thing at a time because I'm a broke college student. but if you have the money to do whatever you feel like then go for it.
also I might look into buying some equipment cheaper from the internet like on sonicelectronix.com or ebay. then taking it to best buy or another local car audio shop to have it installed. Checking circuit city isn't a bad idea either, since they are liquidating their inventory and going out of business.