In case you aren't aware, there are plenty of tutorials out there that help you get a raspberry pi to boot from USB, which allows you to use any HD there is. M

In case you aren't aware, there are plenty of tutorials out there that help you get a raspberry pi to boot from USB, which allows you to use any HD there is. Moreover, nothing stops you from getting everything to run on a RAM drive. There are raspberry pis with 8GB of RAM on the market right now. Having said that, an official raspberry pi SD card with 16GB is sold for 10$. Not exactly something that pushes you to bankruptcy.