A/C starts cold but after a little while, blows warmer air. Any recommendations?

What is your question?

My car has 75,000 miles. This started about 3-4 weeks ago. Initially, I could just turn off the a/c and wait 1-2 minutes then turn it back on, and it would work again. Now, it seems to take longer and longer to come back on. I also think it seems to work better and longer when I am going on the freeway without stop and go traffic. Would like to know what your recommendations are for what tests should be run, and the cost of anticipated repairs. Thank you.