It seems that can buy a perpetual license for GBP £5000 / developer, which is equal to 16 years of monthly subscription (quite optimistic for a 3yo project).
it seems pretty reasonable to charge $30-50 a month for somebody doing the hero's work of reimplementing and building on top of a 30 year old programming environment. also there's a free one! spray money the people who do crazy niche work! that's what makes the world beautiful!
An alternative is B4J, a free (as in beer) BASIC that compiles to Java, so should run just about anywhere. It also has
* B4A - a free version for Android * B4R - a free version for Arduino and ESP8266 * B4I - a paid version for iOS
The main (sole?) developer is ridiculously responsive and helpful.