Your question is kind of vague, you might want to provide some more details.
Note, your profile does not mention where in the world you are living, and that affects what wireless solutions are legal where you live. I assume that you probably don't have a ham license which again limits solutions to those that don't need certification.
In terms of the area, is it open space between where the Arduino is and where the PC is or are there trees, etc that could potentially limit the range?
How fast do you need to transmit data and how much data?
Is the PC on the internet or is it stand-alone?
What kind of budget are you talking about?
Is it for a single day event or will you be wanting to do this in the same area multiple days?
Can you put additional units (mesh routers) in the area to give you more range?
Which type of phone are you using and are you setup with the appropriate android/ios development environment to write the app on the phone?
Are the phone and PC in separate locations?
Now, I am not skilled in doing radio stuff, so this answer is worth what it cost you (i.e. 0$), but off the cuff some thoughts are:
- I you have WiFi available in the area, use an appropriate Wifi shield on the arduino, and use a phone that also supports wifi. If you configure it, you can set up wifi networks that are stand-alone and don't connect to the internet in general, and you could use that in a fixed area
- I saw there was a kickstarter project recently (OpenSource RF - http://www.opensourcerf.com/rfd21815-wireless-inventors-shield-for-arduino.html) that can do point to point communications up to 177 meters
- There is a current kickstarter project (RadioBlock - http://www.kickstarter.com/projects/545073874/radioblock-simple-radio-for-arduino-or-any-embedde?ref=category) that if funded on October 6th will provide Arduino connections to an Open Mesh environment where each device just talks to the devices nearby to eventually route package. Here is a blog about setting up an Open Mesh setup I found via google (http://www.shareable.net/blog/how-to-set-up-a-open-mesh-network-in-your-neighborhood)
- I could imagine tethering an Arduino to a cell phone to give you a connection to the internet, but with cell phones you need to watch the amount of data sent, since cell phones start jacking up the prices once you go over your monthly data limit (typically 2-5 gigabytes).