The prototype board ran me about $20 but it was a 4" x 9" that I cut to size and used for multiple projects.
LEDs are from
www.BestHongKong.com: http://www.besthongkong.com/product_...roducts_id=243
I bought about 30 of them for my dome light and trunk light project, ran me about $50.
Resistors were pretty cheap, about $0.30 to $0.50 each, i bought about 50, enough to cover these two projects and more.
New dome lamps and trunk lights were about $25 and $12 respectively.
So i'd say in total i spent about $115 for the dome + trunk light... but keep in mind, i have lots of material and supplies left over to do more/similiar projects.
I will probably work on my map lights next; they currently have LED bulb replacements in them... not very bright and very blue looking. although, I might tone down the brightness for them... like you said, that much light might blind me while i'm driving.