Upgrading memory on dedicated servers is and always has been crazy expensive. It's absurdly expensive - we had a 4gb Dell server at <big company /> and, if I wanted to double that to 8GB, it was going to be another $50 per month for two years. I could've bought the memory outright for $120. It's around that time that you need to re-evaluate which server you have and whether it's time to change servers completely.