The Dreamcast will forever, and always be my favourite console.
I'm even the creator of the official Dreamcast fan club on the escapist, however it only has one other member, so please join if you want to.
Just search for the escapist's official Dreamcast fan club.
Now, to your questions.
1 - Average price? i don't know in dollars, only in GBP.
2 - Shenmue, Jet set (Grind) Radio, Toy commander, Seaman, Silver, Typing of the dead, Chu chu rocket, D2, illbleed, Elemental gimmick gear, Record of Lodoss war, Blue stinger, Outtrigger, Cannon spike, Psychic wars, Spawn in the demons hand, Sword of the berserk guts rage, jojo's bizzare adventure, Power stone 1+2 (was on the PSP though, but not on any actual consoles other than DC) Project justice, Maken X, Soul calibur, Omikron the nomad soul, Confidential mission, Grandia 2 (the best version, the ps2 version is pretty bad) Slave zero, Virtual On: Oratorio Tangram.
(FYI, I haven't played all of these, but these games are worth looking out for at least)
3 - The disc reading sound is very loud. If you have a PAL version of the console you can play backup's without mod chip. The space on a vmu isn't that big, so invest in at least two. The official dreamcast gun isn't available in the US, though you can buy third party ones (it's worth buying for house of the dead 2 alone). Dreamcast games are suppose to look pretty good on VGA, so if you have a monitor, that's something to consider. Online has been disabled since 2002, however if you can find a hard to find broadband modem you can go onto the scthack server for Phantasy star online (I also hear that their's servers still up and running for quake 3 as well). Import Shenmue 2, and Headhunter, they are worth it. Blue stinger is infamous for being a very love it, or hate it game, so do some research on the game before deciding to purchase it. Oh, and one more thing...the ring: terrors realm frikken sucks!
Okay i think that's all, have fun with it!