Having built products from scratch I know for a fact that selling to the first 10 users is really hard but if you give it to them for free and get the feedback on what didn't work and improved on it - it makes selling to the next 100 people that much easier.
Right now OP is making an assumption that his product is useful. It's a guess. Doing the beta for free for a small set of users validates it with small effort.
In fact the first release should be as minimal as possible. Op can charge those users in the subsequent releases.
I used to believe that but eventually I became worn down by it all. You get so many "opportunities" presented to you that don't turn into anything that you have to take most of it with a pinch of salt.
On the other hand someone who has put their hand in their pocket is going to get a lot of my attention.
Right now OP is making an assumption that his product is useful. It's a guess. Doing the beta for free for a small set of users validates it with small effort.
In fact the first release should be as minimal as possible. Op can charge those users in the subsequent releases.