[andfrob]

What is the ROI for the company buying you?

If it is website traffic... multiple your monthly new visitors by $1.50 or whatever and given them a reasonable break-even period (12 months)?

If it is a team.... what would they have to pay in recruitment fees?

If it is code... what would it cost to build it?

For another small business that is bootstrapped, this is the only way they can think of it.

You get a bit of a negotiation advantage if you can identify what matters to them most and use that as the metric. You can start amplifying how much of a difference you really can make for them.