Here's a banker's advice, I look at these deals occasionally when people want to buy a business with debt:
The business is ultimately worth what you're willing to pay and what they're willing to sell it for, its as simple as that. Once a business is worth/sells for about $25mil, it gets into a competitive bid process and establish a much better market.
There's some metrics to consider, but on a smallish business, three times its annual cash flow is a good starting point for negotiation. Take Net Income, then add back Depreciation and Interest Expense as they report on their Tax Returns. You should ignore any other "addbacks" and also look at officer's salary to see if the wages they're pulling out of the business are equivalent to the time they put in. If a broker is selling the business, they'll practically create "addbacks" to inflate the value.
For example, if you're buying a restaurant and you're going to act as the manager, you shouldn't include the $60,000/year in wages paid to a manager. That's compensation for your time. If they don't sell the business, they have to pay someone else that money to run it.
Is it a business that the seller could potentially leave and compete with you on? How many years will you require in a non-compete?
If you plan on financing it (which I wouldn't recommend), then an SBA loan is going to require a valuation. I don't think they're worth the paper they're written on typically.