My check engine light has been on for about a.

My check engine light has been on for about a month and a half or so, I took my car to several places to find out what was wrong it and they had all told me it was transmissions related. The code number is P0700 and I was just wondering what the exact part is that I need for my car because there are so many different ones for this part that I cannot afford to purchase the wrong part; not to mention my inspection is due at the end of November and the part has not been fixed yet. My car is just a 4 cylinder, basic model. If there is any information about this car problem that you can also provide, please do.