The UC pets, assuming you find someone actually wanting them can vary anywhere from $5 > $50 depending on stats, colour etc. I'm not sure what pets are worth which, but the names seem to be a good format so that will definitely help you. Sometimes more... The accounts themself, if a shell would be worth anything up to about $15 each? Once again, depends a lot on what the avatars, themes, trophies etc are like. (and the prices may change depending on that!)
A shell account is an account that doesn't have many trophies, avatars, site themes, etc. There's nothing too special about them besides their age. Shell accounts usually have nothing in them.. no neopoints or rare items. People usually buy 3 month shells because these accounts can see r99 items in main shops. Or they buy 3 year accounts because they have access to the Almost Abandoned Attic along with other perks.
Around $15-25 per shell. Pets are separate of course, because they can easily go around $50+, depending on stats and rarity.