Ask them "What if in 2 yrs I become so vital that if I leave the company falls apart?" Let 'em know that early back-end engineers have an enormous impact, and you walking could cost them the company, and why wouldn't you, you'd just be an employee with pennies in stake. Then suggest you're open to being a 30% equity stakeholder (co-founder). ;)

Think about it this way, if you ballbark their maximum exit at $30M, and you own 1%, you end up with $300,000. But the chance of that happening are slim. You already make good money, at $85K per year you can save and invest more than $300K in a few years without too much trouble.

Other considerations aside, why take any risk when you already have a sure thing? Whether they offer 1% or even 10% doesn't make much of a difference.