I have seen a HUGE increase in cost. Just about everything is in the $20 (U.S.) price range or higher. The 'core' books for DND will run $90. So, it is a tough call, spend that $90 to upgrade to 3.5 or stay with 3.
Then there are some of the other things out there, like:
Book of Challenges: Dungeon Rooms, Puzzles, and Traps at $22
Complete Adventurer (due out in 05) $30 (when I read the description, I was stunned. Complete Adventurer serves primarily as a player resource focused on adventuring skills for characters of any class. As adventuring is the foundation for the entire D&D experience, nearly every aspect of the D&D game benefits from the material in this product. will this REALLY be worth $30?)
Characters have access to new combat options, spells, equipment, and prestige classes, as well as exciting new character classes such as ninja and scout. Complete Adventurer also provides new information on several organizations and guilds, and Dungeon Masters will find material for creating or optimizing single creatures or even entire campaign worlds
The list just on and on. I read some of the descriptions for these products and I am just stunned at how outragous the cost is compared to what is inside. I look at the nice large font size, the standard items in each thing: feats, skills, prestige classes. It seems like each and every supplement HAS to contain them. Is that a bad thing? eh, just seems like too many resources to get to if you are trying to remember where you saw a particular skill or prestige class. I am sure, one of these days, they will be publishing a book with ALL the skills, feats, and prestige classes.
With all the high prices, the last time I got anything was at a WOTC store that was going out of business and got some nice deals.