I hope none of these are serious because some just sound like tat. Let's fill some out as Steve O'Luckless, the rich yet embittered retired brewer from Ireland (brewing potatoes or something):
$5: Your name is added as a random sentient historical figure at the beginning of worldgen. You have a chance to see engravings of yourself being eaten by a dragon, or becoming lord of an empire.
There is always someone named Steve O'Luckless, or (more likely for $5), Dicks McCock Boobs. Everyone else has an RNG name except for a mysterious bank of people who always show up identical. It's not like this will detract from the randomness of it all.
$25: Crayon picture (probably a copy)
A copy? Shame! Steve is sad now.
$50: DF Shirt or hat
Sewed personally by Toady's aging grandmother, her fingers working vile curses upon her kin and you as she tries to forget that she'll be paid far below minimum wage for this.
$75: Signed DF poster
Steve is happy and hangs it in his room.
$100: Your name gets added to a list, from which the names of Fluffy Wamblers will be chosen. All Fluffy Wamblers will have a name, drawn from this list. Special thanks mention. Limit 500
Why?! They're not even real creatures! They're vermin!! And they'll all be named things like ILIKEVAGINAZZ and xX69internetXxx! Except for Steve the fluffy wambler.
$250: Towns in worldgen can be named in your honor, civ of your choosing. Limit 50
This is even worse! Because the naming pool is even smaller, pretty much every town Steve visits will be named Steve!
$500: New animal you get to describe and name. Subject to approval, obviously. Limit 25
Oh, this is subject to approval but naming 2% of all towns isn't?! And how can you choose a civ when civs are randomly generated? Do you mean race?? Anyway, Steve likes potatoes a lot and has added potato men to the game. We're doomed.
$1000: A new "vein" stone is named after you, color and properties of your choosing. Limit 10
"Realistic geology with certain fantasy aspects? Pah! I'm looking forward to a collective union of trolls saving up enough to add penis ore to the game! And it's fuchsia!"
Seriously, though, you underestimate Toady's integrity. He's not famous and he's not going to let random people on the Internet make him add stuff for a small fee.
$1,000,000,000,000,000,000,000,000,000: Death to all fiat currencies achieved
$1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000: Bitcoin Revolution
$1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000: Rape Dollar$ accepted as currency