Prices have definitely gone up. It was common to get a decent stave, usually with the sapwood off, back sealed for $40-70, for many years. Not just with ebay, but over the last 20 or more years prices stayed flat, despite inflation.
I hate paying more than I have to, but the higher prices are a more accurate reflection on the worth of a nice osage bowstave, especially with all the extra prep work.
There seems to be a line with some semi/pro bowyers. They charge $300-400 for a decent finished osage or yew bow, despite the retail value of the stave, which they may have gotten for free(nothing is really free, when you count labour, haulage).
Many bowyers really under value the price of their materials and labour, when compared with other craftsmen, such as luthiers, cane fly rod makers, or even fg bow makers.