Well got the 0705 and 0707, so if I just change the rear OS will that get rid of my Evap as well? and where can i get an OS for a decent price?

 

no it won't get rid of your evap. Try resetting the codes first to see if they come back. If they do then do the evap first.

 

how much is the Evap?

well this is the first time that I've gotten the code for it... but its not the first time my SEL came on, I think its because I replaced my Ypipe, it use to come on and show 0505, but since I replaced it today, its the first time I've gotten 0705 & 0707

 

Get this O2 sensor: http://cgi.ebay.com/ebaymotors/NEW-B...temZ8057792500

Or

http://cgi.ebay.com/ebaymotors/NEW-N...temZ8059920754

I had the same codes as you have. I installed the rear Bosch O2 sensor but the codes didn't go away, so I reset the ecu.
The Evap system is not related to O2 problem. After you fix the O2 sensor and recet the ecu , check for ghost codes after couple of weeks, usually the 0705 code is paired with another Evap code which points to the main problem. In my case it's 0903 Evap canister vent control valve (it shows up once every few weeks and disappears). I took the valve out and put oil inside but the code appeared again). I think I will replace the Evap canister .

 

how do I check for the ghost code, because I only got 0705 and 0707, if I replace the OS will I get the EVAP code along with another one then?

 

Oxygen sensor is not related to Evap sys malfunction. If you replace it or not it will not affect your Evap codes.
Just check for your codes frequently, because 0705 could be a problem in a lot of things in Evap sys and you don't know where to look. Read the stickies about this code, it says that usually 0705 will be paired with another evap code that points directly to the problem. So if you don't have any other evap codes it's impossible to find out the location of malfunction.
Reset the ecu and when cel returns check for codes again and may be you will see additional evap code.
My second evap code was turning on and off every few weeks so you just have to catch it while it's on.