Paid about $70 for Karous in 2014.
Paid about $65 for Shenmue II PAL in 2001
Everything else for DC has tended to be about $40 for rare games like Radirgy, or much much less for the common releases ($5 Sega GT/Sega Rally/Metropolis Street Racer, etc.). A shame prices have been getting absurd lately, but I think it is only going to get worse for those more rare dreamcast games over the coming years. Simple supply and demand, DC games are a fixed supply, whereas I don't see the retro gaming demand for DC titles falling over the next 3-5 years. I'm looking at the Sega Saturn retro game market as an anologue of where the DC might be in 3-5 years - common games might get a slight nudge of a few dollars, but still be very affordable, whereas certain and well regarded more rare games will regularly exceed $100.