Help with wireless application!

I'm trying to get an arduino to interface with a serial computer application i wrote. The application reads information from any serial (COM) port on the computer, and works fine (It will already read things from my arduino while it's attached with a USB wire) However ineed it to be able to interface with the computer wirelessly over a range of +300 meters (So bluetooth is out of the question) how will I accomplish this? It can be one or two way, whichever, but ideally I need the cheapest, simplest solution. Can anyone help with what parts I will need, how to put them together and where i can but them? I'm using an arduino Nano (NOT pro-nano) Thanks!

Sparkfun has a number of wireless solutions, and a table comparing cost, range, error handling, ease of use, etc. Might be a good place to start.

Once you have chosen the hardware, we can help you get it connected to the Arduino.