With $300 u might probally get some door speakers, cuz everything audio related cost big $$$ i spended about $500 for a kenwood 400w amp and 4 wenwood speakers. $400 for mu indash, $300 for my 12" kickers w/box, $160 for sony amp, $220 for rockford fosgate capacitor and all connections. All that adds up to about $1580... And thats only for a nice lil sound system.
If u dont know how to connect any adio related stuff, or dont get it installed for free...... u going to spend big $$$ for that too.