Permit costs do vary across the two countries.
Rwanda permits are $1500 per person (minimum age of 15).
Uganda permits are $700 (minimum age also 15).
Visitors to Uganda are also able to book permits for a longer gorilla habituation experience, which lasts for 4 hours. Again the minimum age is 15 and the cost is $1500 per person.
Accommodation prices vary depending on which country you choose to visit, however accommodation options in Rwanda are more exclusive and in-line with the permit prices.