You can actually do it yourself. Its no more work than doing a transmission service. Pull the pan. Take the T25 torx bit screw off to get the sump filter. Take all of the 8mm bolts loose that you see on the valve body. Make sure you get the plug loose on top the valve body on the outside of the case. Dont take the shifter cable loose so it can keep your linkage aligned to ease in reinstall of the body. When you get the valve body out, you will see the big solenoid pack on the valve body. Flip it over and you will have to guesstimate the area of where all the torques bolts are that hold the solenoid pack on. Now take all of them out, like i said , just make sure you take out only the bolts you need, if anything do what i do and loosen them off about a 1/4 in and see if the solenoid is loose. When you put the new solenoid on, just hand tight . When you put the valve body back in just start a couple of the 8mm bolts. and tighten them up after you get them all in. Just make sure you dont move the slot where you linkage slides into the valve body or it will be a little harder on you.
I would go to an independant transmission shop and see the price on the solenoid pack. The dealership usually has them for about 376.00 But i think you can get them cheaper. You will need it for a 545 RFE transmission. Make sure you disconnect the battery before you start to help when you get done changing the solenoid.