Cool - a Powerbook 180 was my second Mac (bought it new back in '92), and I loved it. It was a tank, pretty much indestructible.

Enjoy it!

As for finding RAM, I'm guessing the cheapest and easiest way is to scan eBay for a 140/145/160/165/170 or 180/180c advertised with 14MB RAM (meaning it has a 10MB module installed), and some kind of flaw. That, hopefully, would enable you to buy the unit cheaply.

If you could find new-old-stock, or even used, RAM modules by themselves, it's likely they'd cost more than an entire used Powerbook with the RAM already in it.