I am having hesitation problems with my 2004 Mazda V6 sportsback (110k miles).

I recently went to Firestone to get an oil change, after that the car hesitates randomly when I accelerate, so it happens I would say maybe 1 in 5 times when I try to accelerate the car.
When I push down the accelerator it hesitates and the car jerks like the fuel is either not igniting completely or is not reaching the cylinders. As I keep my foot on the accelerator the car hesitates a few times then begins to accelerate.

I took it to Pep Boys and had them do a diagnostic which they charged me ($90) for which I could have probably used to buy the computer with which is ridiculous.

The following codes came up:
PO302: Mis Fire 2 CYL
PO421: CAT
PO455: Evap Large Leak

The guy told me that I needed a new coil for the 2nd cylinder which is supposedly in the back of the car and would take around 7 hours to fix and cost me around $400. He said after we fix that then he can take a look at the other two problems.
I know that the CAT code was coming up for a year now because of the O2 sensor but the car has been driving fine until I got the oil change. I had them use high mileage oil and last time I used synthetic blend so I am not sure if this could have caused the issue also.

I would appreciate any help as I can't afford to spend that much money and don't know too much about cars.