Saffron and paella

In order to cook Paella (a delicious Spanish rice dish) I needed to buy Saffron spice.  It was hugely expensive.  So, I've decided to start a business of growing saffron and becoming immensely wealthy.

How long will it take me to make my fortune? This is a very rich task involving conversions, patterns, spatial reasoning and modular arithmetic.  Great for a class activity or challenge work for high performers.