Go for quality over quantity. You need one pair of pants that feels good. That’s it. If it’s something expensive, splurge — better to have one pair you love than a few that don’t feel great. The type of pants depends on your lifestyle; maybe you want a pair of jeans because you can wear them around work or home, or some other kind of skinny pant because your office is less casual. I’d stay with something slim, though; wide pants aren’t as flattering when you’re pregnant.
The great thing about being pregnant is that some of your friends are probably at around the same stage in their lives. Maybe when you’re done with your favorite pair of maternity jeans, they’re really just getting good from being worn and washed, so you give them to a pregnant friend, and then later she can offer them to another friend. Make it a funny thing — take a picture of yourself in the jeans, put it in the pocket, and then pass them on.