The pricing is a bit odd but this is what the dev has said.
The latest version costs $ 10 at the time of release, then after 1-2 weeks the price drops to $ 5. As soon as a new version of the game is released, the previous version of the game drops in price to $ 1, and the other previous version becomes free.
Example:
0.6 at the time of release was $ 10, now it costs $ 5.
0.5 costs $ 1.
0.4 is free.
So if you paid $5 you'll get access to this new version in a couple weeks. It's like a tier thing. You're in the $5 tier so you get the game when it is made $5.