What's the risk of selling old MacBook with data?

I have an old MacBook Pro I'd like to sell.

2.4GHz Core Duo/2GB/256MB

VRAM/200GB

5400rpm

I've already transferred the data to my new MacBook, so that's taken care of.

The problem is, now it doesn't boot up anymore (it only goes to the screen with the spinning wheel on boot as far as I remember - someone borrowed my power cord and didn't return it, so I can't check anymore), so there is no way for me to erase the data.

I checked with a local Apple Service Provider, they charge $50 for a low level erase, and $50 to install a new operating system.

My question is: Is that even worth paying?

How bad/dangerous is it to just leave the data on there and sell it to someone/at one of the sales websites?

Thank you for any help and advice!!