If I were you, I would get a decent pair of bookshelves, and then build up piece by piece. You can utilize a phantom center effect for the time being, and this is the progression I would follow: L/R > Sub > Center > Surrounds.
If you are just looking at one pair of speakers for $300, you have a lot of good options: http://www.avsforum.com/t/1514586/list-of-interesting-bookshelf-speakers-100-350-pair-prices-and-links-no-reviews
Alternatively, you could go with a pair of bookshelves and a sub, something like the Pioneer BS-22 and BIC F-12 would be a good 2.1 system to start with. Then add a Pioneer C22 center and another pair of BS22 for surrounds.
If you are just looking at one pair of speakers for $300, you have a lot of good options: http://www.avsforum.com/t/1514586/list-of-interesting-bookshelf-speakers-100-350-pair-prices-and-links-no-reviews
Alternatively, you could go with a pair of bookshelves and a sub, something like the Pioneer BS-22 and BIC F-12 would be a good 2.1 system to start with. Then add a Pioneer C22 center and another pair of BS22 for surrounds.