When I ask clients about their budget for a kitchen renovation, or a living room re-do, or anything, 99% of the time they respond,
“Well, I don’t know what my budget is, because I don’t know what things cost.”

That may be true. But you still need to know how much you will be comfortable spending.
Here’s a trick I use. Say this sentence aloud: “I’m willing to spend X on this project right now.” Plug in $100, $500, $1,000, $10,000, for X – whatever amount makes this a true statement.

Now add 5% or 10% to X and say the sentence again. So if your first sentence is, “I’m willing to spend $10,000 on my house right now,” Your second sentence could be, “I’m willing to spend $11,000 on my house right now.”
Is your second sentence true? Sit with it a moment. Check in with your gut – how’s it doing?
If you’re still feeling good, say the sentence again, increasing X by the same amount of money.

Eventually, you’ll reach a point where you’ll think, “Wait, that’s too high. I’m not willing to spend that right now. The last amount was ok, but not this one.”
This is really effective when you’re house- or apartment-hunting. I may have mentioned at some point that my mother-in-law is a realtor. Every once in a while a client – hers or another person’s – will fall in love with a place, and they’ll say, “I want this; I don’t care what it costs.” Well, guess what? They do care. They just don’t know it until that magic, just-a-little-too-high number is on the table.
This sneaky little exercise can trick yourself into finding that magic number for yourself.
The REAL trick is sticking to it.

Thanks, xJavierx, for including these fabulous kitchen, first living room, library, and second living room pictures on your Flickr photostream.