Windows DO contribute to a room's value. You can either use windows or statues for the new "wall" after you dig one out - just be sure to leave supports. Windows attach to the nearby walls (so they don't leave the little pillars) and look better than statues imo, but both will work for rooms.
If you want a very cheap window to fill the gap in a room that you don't want to be valuable, cut 3 green class gems with a no-skill jeweler and use them as a window. It's only 30 value instead of 50. I did this for a few rooms that happened to have expensive gems or ores in the walls and were too expensive.
-edit- also, when it comes to regular rooms, you really don't even need walls. I usually just build big sleeping chambers with rooms sized down to little +s, this leaves room for a cabinet and a coffer and yet leaves the room very cheap. Un-smoothed floors comes to 27 rent with a base quality bed, cabinet, and coffer. Even with the 5 floor tiles smoothed, it's only priced at 35. That is WAY below the usual cost of well over 100. Plus, you don't need doors - one big sleeping hall works fine. The layout I use is this:
code:
▓▓▓▓▓▓▓▓▓▓▓▓▓
▓▓▓▓.▓▓▓.▓▓▓▓
▓▓..B...B..▓▓
▓.B...B...B.▓
▓▓.▓.▓.▓.▓.▓▓
▓▓..B...B..▓▓
▓.B...B...B.▓
▓▓.▓.▓.▓.▓.▓▓
▓▓..B...B..▓▓
▓.B...B...B.▓
▓▓.▓.▓.▓.▓.▓▓
▓▓..B...B..▓▓
▓.B...B...B.▓
▓▓.▓▓▓.▓▓▓.▓▓
▓▓▓▓▓▓▓▓▓▓▓▓▓
With 'B' being the beds, '▓' being the walls (and pillars), '.' being the floor space for the rooms (can put cabinet + coffer in here beside all the beds). You can detail all the walls with no price increase - none of the rooms use the walls. None of the rooms overlap (you could overlap them if you wanted even cheaper rooms, but that can cause problems when the economy starts). This is just a 20 dwarf example, you could expand it as big as you want, since it has built-in supports (way more than needed, but I like the way it looks - you could knock a few out and add in high quality statues and animals in cages, these would give happy thoughts to the dwarves as they passed by them, and wouldn't affect the room prices). You can just put the entry halls to it anywhere, none of the rooms rely on the walls so it doesn't matter.[ March 24, 2007: Message edited by: Paul ]