Why would a simple Iron Door cost 500 gold? That is not in line with other mundane equipment stuff.
So, per the downtime rules, rooms include doors ("Unless otherwise stated, each room includes a floor, ceiling, walls, furniture, doors, windows, and other details that are appropriate to the room's purpose in your building... Exterior doors are good wooden doors with simple locks. Interior doors are simple wooden doors with no locks. You may install different locks by paying the normal price for locks."). We can see the price of a given room in Goods, which would indicate the materials used to create it. Furthermore, we can see in the regular downtime rules that purchasing a Good outright is 20gp (or 10gp if you spend time earning it, but you seem to want purchase cost so I'm going with 20gp). From there, we just need to figure out how many Goods a simple wooden door would equate to, and from there we see how much they cost. Looking at the room descriptions, I found the Altar room which is 2 goods and is basically just the altar and nothing else. It seems reasonable to say that the altar portion takes up 1 of those goods, leaving the remaining 1 for all furnishings (door, maybe windows but the description doesn't mention any). From there, we can see that the price of a simple wooden door (without any lock) is at most 1 good, and therefore at most 20gp. As a result, I'd just say a simple wooden door is 20gp and call it a day.
Is the question about the cost of buying any old door, or buying a door and having it installed in a doorway?
I'm glad the doors in my house don't way 125 pounds...
I spent a day one summer in Georgia carrying about 80 doors. Most of them were front doors of old homes built before the Civil War. Back when plywood didn't exist and hollow-core doors weren't invented. In other words, these doors were big and solid, made of oak and ridiculously heavy. I could carry one but it was difficult so we had two guys carry them, but we carried two at a time. Heavy, but doable.
Those would not be simple wooden interior doors. They weren't noticeably strong, so I'd call them a good wooden door, but they weighed about half what the OP quoted here.
Aside from the weights being off, I think the upgrade pricing is fair in an abstract sort of way. But the initial pricing before upgrading seems lacking.
If the downtime rules are valid, and the 20gp assumption is valid, then having a good door be worth 26x more than a simple door seems to be too much. But that seems to be the most in-line with the rules presented so far.
Don't tell my players. They'll start hauling dungeon doors back to town and blow the roof off of their WBL progression...
Of course, as we learned in another thread that's currently raging on page 1, nobody in town can actually appraise their value properly anyway...
Typical dungeon doors are a bit bigger than what we usually think of as door sized. 8' tall and 5' wide, which is a lot of door.
I have always found there is no need to buy doors, as you encounter them in dungeons all the time and if you want one, just cart it off.