My insulation was $400ish on sale (buy 3 get 1 free) and my poly/tape/acoustic sealant was $110, all bought at Home Depot. That is for a 24 wide by 24x26 deep and 13 foot high high walls. Just side and front, roof and back wall (attached to house) were done for me. And ya, the insulation is so easy I would never pay anyone to do it, just takes time. Just make sure you got a good mask and some gloves, wear long sleeved clothing. The poly is a bit trickier, especially with that messy sealant, but after you butcher part of one wall the mistakes are made and lessons are learned. 3/4 of the garage looks professional at least
It helps to have an extra person to hold the poly away from the area you are applying the sealant on, then go back and push it in nice and neat while they hold the other end. That worked way better than trying to apply it as I went. The ceiling would be a bit of a pain though.. I never had to do that so I can't really offer and advice.