$50 seems a good price (are we talking US dollars here?)
For about that price you can get them original factory sealed (
eBay link), but since you'll be playing them and taking off the seal it doesn't really matter.
I say go for it - $50 is a good price for both in mint condition and you're right, they're pretty hard to track down in good condition these days.
Finding it with the box is hard enough, but for me it's gotta have all the instructions and booklets and be in mint condition.
I bought Silver factory sealed off that seller above (since I lost my Silver version) and the memories it brought back when I pulled off that Nintendo seal...Ahhh, childhood.
I agree with you - G/S/C are the best generation of games. I love 'em to bits and trying to track down Gold (probably use that eBay seller) and Crystal in good conditions now so I can have them all nice and complete. I'm anal like that.
