What Conversion Rate I can Expect From an Email List?

It depends on soooooo many different things ...

Traffic demographics (that's a big one), their expectations, what you've shown them so far, what you sent them for signing up and whether it contained a promotion at all, whether they opted in through a squeeze page or a content-rich site (this typically makes a very big difference to conversion-rates) or something in-between the two, whether they already know about the product/service you're promoting, how closely targeted they are to exactly what you're promoting (that's a huge one), what you send them in the intervening emails before the first promotion, what the open-rate is, whether they're on 16 other marketers' lists (in your niche, they probably are), and I'm only just warming up, here: I haven't even got as far as thinking about the sales page for whatever you're promoting yet ...

Seriously, nobody can answer this question meaningfully and constructively without knowing a whole lot more about your business and your traffic.

Personally, I'd instinctively be a little wary of anyone offering you figures.

Just give it a try and you shall see, then adjust things on the go.

However, I think you shouldn't be expecting anything big at all, considering that all your e-mails are from people who subscribed for a freebie. Next time try to put on price on it, even if it's very, very low, this pay you'll be sure that your subscribers are people who touch their credit cards, at least from time to time.

It depends on various factors like what others have said above. It's only when you do some testing, then you'll know.