Qt for Application Development Professional (ADP) is 3460 €/Year.
If you're making something which you sell for $50 or so you'd need 100 sales per year to just pay for the development environment. That also assumes that it took you less than a year to make said product.
I guess that is just one of the many risks you have to take if your trying to build a business. A couple of hundred dollars in licensing fees are not going to sink your product. For a side project that you don't expect to make any money it might be too much, but in that case you could just as well open source the project.
If you're making something which you sell for $50 or so you'd need 100 sales per year to just pay for the development environment. That also assumes that it took you less than a year to make said product.