Oh dear.....
..its the how long is a piece of string question. Hope to give you an indication tho as Im helpdul like that.
Ok - for example...
A Fat Titanium would set you back round about £600 I think for a frame (approximate)
Kona Hei Heis we have seen on Ebay tend to go from £400-700
(although Ive picked up Hei Heis for 200, 300 and 350 before)
Merlins can go from anywhere again from the £500-700 mark
(Havent seen one for sale in a while tho)
Anything else lush and ti-like around the same figure...
Cheap ti (lesser known brands) can be picked up for £200-£350 I imagine.
Most of these figures are just my rough guessing really from what Ive seen on classifieds and on ebay.
The addition of a disk mount or 1 1/8 headtube versions tend to go for more as they tend to be more versatile in the modrn kit world.