My suggestion is to have ti pumped out in the water. West Marine, and internet have vacuum extractors which allow you to put a tube down into the oil sump. I used one of those on my last oil change on the 150, and less than a couple of oz was left, when I opened the drain plug. You can change oil filter every 200 hrs--same with the lower unit.
If you have to haul the boat on a travel lift, block it etc that is going to be pricey.
If there is a C Brat in the area with a 25' trailer who would volunteer to let you use it for a couple of hours, you could do a change in the parking lot--(and that would include a lower unit (but should have new o rings).
Typical is about $200 or a bit more. for a shop. If you have to use a lift, it may be closer to $500. There is a looper who I told could use my boat lift and we would do the oil change at my house, including the lower unit.
If you were running all at displacement mode, I would say skip the 100 hr, and go to 200 hrs. But you have been making tracks.
Quick internet search shows Carolina Beach Boat Yard & Marina. They have a travel lift and advertise outboard service: ( N34 2.533 W077 53.531) 910-707-1007.
BellHart Marine has a Cape Fear yard, and do Yamana and Mercury outboards. 910.452.7878
Give them of them a call.