How to charge for my extension?

Hi, I'm building www.BuyLocalized.com. It's a browser extension that overlays Amazon with information about where products come from (right now just the USA). We built this because we were pissed off about China and didn't want to buy stuff from there, and it was too hard. I'm looking for some ideas on monetization.

Because we have to do a ton of research the extension needs to generate quite a bit of revenue to have a chance. Building it is a half year project for 4 full time people, and maintenance will be 1 or 2 full time jobs. I've been trying to figure out a way to monetize and I wanted to bounce ideas off of people here. In order of best to worst:

1. Subscription. We are thinking we will show our users 5 or 8 products for free, and then you need a yearly or monthly subscription to see more listings than that. 5-8 products is a workeable amount, so subscribing wouldn't be mandatory. A big issue is this requires a lot of products. We are researching already but for some categories there won't be enough products for the premium version to show anything, and if we expand to other countries then for a lot of them there won’t be enough options that exist to make it worthwhile.

Pros

• Our interests are aligned with our users.
• It is easy to implement.

Cons

• It won't be much money. I haven't researched on what other companies
  experience, but I imagine this won't convert very often and we would need
  an enormous user base to support the team.

2. Affiliate. We could add affiliate links and collect revenue when people buy something. Amazon won't let us collect affiliate revenue from them for this extension, not 100% sure but almost. So we would need to research and add other companies tot he extension, and that has a lot of negative effects on user experience. It would also take a long time, if we did go and add thousands of other companies, we would need to make deals with each of them and it would be a huge task.

Pros

• It would be lucrative. The people who use our app are buyers, the
  average prime holder spends 1050$ a year on Amazon. Affiliate deals for this
  type of stuff is 5-15% usually I believe.

Cons

• Interests with our users aren’t completely aligned, as we would want to
  show them products we get a cut on.
• Exceptionally difficult to implement, as I understand it currently we would
  need separate deals with thousands of companies.
• Our extension may serve as a product discovery engine, so people will use it
  once then buy direct next time, which could potentially result in us getting
  a lot less sales than we expect.

3. One time sale. This just seems clearly worse than the other options, but maybe it’s not?

Pros

• Simple

Cons

• If the extension fails then we would abscond on our responsibilities.
• Only make money once
• Need a constant flow of new people
• Need to convince people to buy before they use it, which may be hard.

Another point is the cost of getting new users. Currently it costs 3$ to get an install of our currently free extension through paid social channels. I am confident that I can get this down to 1-2.5$. This is a breakpoint for the project, if we can get our lifetime spend from an average user above this we can advertise. This is the shining light of the extension I think. We’ve got 250 users currently, and we’ve had almost no uninstalls. People have seen/used our extension 100’s of thousands of times, though it is just a little box on Amazon. We’ve gotta find a way to generate 4-5$ in revenue over the lifetime of a user. I think that’s going to be hard, but I’m hopeful there is a route to it.

I would love to hear from other people! I’ve never built a SaaS project, and haven’t had to think of how to monetize something like this before.