I think it's perfectly reasonable for indie dev's to ask for payment from time to time. And considering how cheap the asking price is, matched with the quality of the game I'd say it's a steal.
To give an example from a different medium for comparison:
The average film ticket price in the US for one viewing (minimum runtime being 90 minutes as an example) is $10-11. That's about 11-12 cents per minute.
In contrast, for a maximum (estimated) runtime of 60 minutes (counting retries) you are paying the equivalent of 2 cents (maximum) per minute.
And while I agree it would be great if it were free, I also know indie dev's have to make some form of living from time to time. And I've seen indie titles priced at far higher ranges that aren't 2/10ths this games quality, so I'd say we all lucked out on the asking price being this generous.