You may already be familiar with Jim Kukral‘s Scratchback service. It’s a widget you place on your blog that lets people give you a monetary “tip” and then their text/link appears in the widget to everyone for a period of time (as designated by you, such as a week or a month). You specify how many links are available and how much they are — so you could have 5 links that are $25 each, and the donor’s link would then appear for 1-week.
I think there’s another interesting opportunity here — either as another function of this widget, or for someone else to create their own similar service. I’d like to see a “roll” of contributor links that are basically auctioned off to the top bidders. For example, I’d be able to specify that 5 spots exist and the price starts at $0.01. Someone bids $0.01 with their text/link and it appears in the top slot. Someone else bids $1.00 and their text/link appears in the top slot, while the prior link drops a spot. Someone else bids $2.50 and their text/link appears in the top slot, while the prior link drops a spot. And so on…
You’ll have to work out all the details, but I think you could receive a full PayPal payment of whatever the user bids, but only require them to bid a dollar (or $5, etc) above the virtual high bid. Thus in the example above, the top spot would really be $2.00 [if you have to bid $1 more than the prior bid], but since the other person bid $2.50, that person would remain in the top spot if this user bid $2.00 [and the $1.00 bid would drop a notch].
You could have it reset at the beginning of the month if you wanted. Also, the benefit to the early bidders is that they could potentially stay up in your linkboard for a lower cost than those after them.
Thus it creates a bit of competition and the market (your readers/advertisers) will determine the true value of those link spots on your Site.
Sidenote: BTW Jim, where’s the affiliate program for your service? 😉