I've been thinking about purchasing a used RDX, however I
was told that they cost a lot more to repair and maintain
than Honda's. I know that they are considered the luxury
brand to Honda but I assumed normal maintenance would
be similar in pricing.
Normal maintenance should be about the same, just steer clear of the dealerships, any good independent shop can do the same job for a lot less money and may even save you from unnecessary work that the dealer always tries to push on you.
I am sure they share a lot of the same parts.