For my first road bike I spent $100 (this was in the 70's). Several bikes down the road, I am now having a custom bike built for me and most likely it will run around $4500 (frame, fork, components - I already have wheels but that would add another $800). I have been riding for some 40 years and don't think that is too much to spend at this time of the life and given my passion.

If you are looking for a good entry level road bike (not a sport or comfort bike but something you can actually race with) you need to spend around $1000 - 1500. I think Components are a real issue and I would never recommend anything less than Shimano 105 but Ultegra is better (and equivalent Campy and Sram). I question spending more than $3000 on a production bike when you can get a custom bike in either steel, carbon or ti for less than $5000. But some people like the fancy look of Trek's or Specializes race bikes.

For a mountain bike you get alot for around $1500. For alittle more ($2000) you get full XT and Fox shocks and forks and the bike for last a long time and perform well. You can buy a $3500+ bike but then it's just to cut weight. Personally I see no performance difference in XT and XTR. Same goes with Ultegra and Dura-Ace on a road bike.