I explain the thoughts behind the price a little in this comment: https://news.ycombinator.com/item?id=22625906
EDIT:
> From my survey I know that organizers pay more than $ 200 for a order management system (e. g. about $ 300 for the system and more per device needed).
I would like to add that this is the price for two days of rent.
> It's too complex and resource intensive for an indie shop, it's not worth it.
If you're not an existing system, the client interfacing and employee training has to be factored into the costs on both ends. If your demo can't cover the client's needs to a tee, that's either an immediate deal-breaker or you have to build more features just to get considered. Then you have to market your product, do customer service, and do sales.
If you take that all into account, your product is not worth it for you nor the client.