Not much difference between the two in cost. Both are horrendously expensive but since there is only 2-2.5# of material in the frame material costs could triple without doing much to frame pricing which has more to do with manufacturing costs and R&D and what the market will bear. Judging from the trends, carbon is definitely on the upswing as a frame material. Carbon frames are very tough but their impact resistance, though large aint nothing like Ti which is the closest thing to a lifetime frame among present materials. Of course Ti will dent where carbon cracks but hits heavy enough to destroy a frame are likely to be pretty damaging on your 50+ bod as well so I would not be too concerned over frame material.
You realize that you are in the $2500 and up (way up) range with these materials for new bikes. No one really knows what the life span of a carbon frame is because the manufacturing technology is continually changing and definitely improving so any statement to that is opinion. The rate of technology transfer from aerospace to bike making is fairly high and planes are a lot more hostile environment than you will ever be on your carbon steed.
Steve