Ask HN: How would you proxy for sales conversion rates?

I'm a software developer working on a (non-software/non-technology) line of consumable products that will require significant capital costs to even do a sample production run. Given that, I'd like to test the waters to try and estimate metrics like customer acquisition costs and whether a given product will actually sell before investing the capital. Based on what I've learned here, it seems to me it would be a good idea to put up a landing page of some sorts and maybe drive traffic to it with an Adwords campaign but what sort of conversion would you guys use to proxy for a sale given that I can't actually sell the product without having produced it (or even having invested in the branding yet)? I supposed I could have people sign-up for a newsletter or something but I would really have no clue how that conversion rate might convert to a sales conversion rate. I'm just getting up-to-speed on digital marketing so any pointers to key background reading material on running exploration tests like this to test business ideas before investing in them would be greatly appreciated as well.

Thanks.