This might not help much but we just finished up the truss layout/design options with the truss manufacturer and the cost was about 20% higher per truss for vaults or tray ceilings.

I went round and round with this question. I ended up doing the ceiling the same color as the walls. It was high enough to accomodate lots of color. I think it's 16' at it's highest point. Mine are more sloped on the side and I have beams but here's what mine looks like. The painters still need to touch up the paint.

I think renters do appreciate a well-maintained, thoughtfully painted home. I live on a street with several rental homes. The homes that look updated, with the exterior in more current colors and the interiors with colorful (but neutral) paint rent FAST. The other homes, which are cheaper and the same size but very outdated with the exterior paint colors and white interiors stay available longer. And not to be contrary, but our LR is painted a color called Navajo White that looks remarkably similar to the one in the pic. It's nice for when the sun is coming through the windows (ie early morning). They face east and a very shady south, however, so the rest of the day the room is dark and dreary. I'm hoping we re-paint in the next year or so, and I'm going with a medium or dark value color...I do not think light colors do anything for a dark, low natural light room.

I like to give some idea of costs even if it is a guess. We were quoted $1000 a foot a few years ago for ceiling height increases. On a 2000 sqft per floor house. Relatively low cost of building area. Framing is cheap upcharge. Cladding varies - brick more expensive than siding. Drywall and paint aren't much. Windows need to be bigger which is variable based on window quality. Cheap windows might be $50 more each or it might be $200 more each. So the number of windows and quality matter a decent amount. Now - you are talking varying ceiling heights. Ranch? We had it with a 2 story so then we had an extra few steps upstairs. That costs some money but it wasn't bad. HVAC load increases a bit. Insulation costs a bit. Here is the thing - most cheap new construction has high ceilings which shows you it doesn't cost that much. Or people really like it. Take your pick. Personally - in that size room - don't go over 10. 10 feet from 9 everywhere else is a subtle change and may not get really noticed. We had 11 in great room and 10 in others. It was subtle and I doubt people noticed but it gave the room a grander feeling. It was 20x24 or something in that area. This time we are doing a type of vault - flat peaked I would call it. The ceiling is split in 3 equal parts. 2 are sloped and the middle is flat. 13-14 feet at the flat part. Nothing above it. Not seen that often around here which we liked.