Aries PCs are decent, take a look around their site, however I picked one out - click here its in your price range and its spec isnt bad.
You could also try Dell, they often have decent deals on.
There will be other people who will have other suggestions for computers... If I can think of, or come across anymore ill post back.
Regarding your second question, you dont need to pay another 14.99 a month, you just need to use a router.
By using a router you can use more than 1 computer on the same internet connection.
Although, it depends on what you currently have. If you could post what type of modem/router you have now, i.e. make and model it would be more helpful.