P2243 - saturn vue 2005

Question

Hi, Had code p2243(voltage circuit) for 2005 Saturn vue engine size 3.5L and had the sensor replaced with our local mechanic. Within a few days code 455(evap systems gross leak)was detected and I was wondering if maybe during the replacement of the other sensor something could have been damaged. I got a copy of the description of possible problems, we replaced the gas cap and checked the emission hoses on the engine and they're ok. So know my husband is trying to replace the solenoid and there is a confusion because the auto parts quoted $224.00 for the part and he looked up on line and they range 25-30.00 but isn't sure witch one to get.
I would be grateful to get advise. We already spend more than we can pay for parts and labor, and my husband is trying to do the repairs. Thank you, sincerely, desperate mom without a car.