I'm sure your hunter instructor will understand. You won't be the first person to quit her classes! Just explain to her that you're interested in trying something new, but if you ever want to take up hunter again, you'll give her a ring:)
I personally LOVE Pony club. I'm 19 now, and still going strong! I love it too much to quit. It's a lot of fun, definitely worth doing. And the gymkhanas are great! I've starting instructing the smaller girls now, so it's great to put on my resume.
I am only just buying a trailer, and I've been at pony club for years. You will need to either borrow one, or get someone to transport your horse for you.
I hire someone with a big truck to take my boy- it costs me about $30 both ways, so it's not too unreasonable.
You could also ask around at pony club sign on, and see if anyone has an extra spot in their trailer, and if they would be willing to come pick your mare up.
I can't tell you anyone around your area... I live on the other side of the world! Haha.
I have done some eventing before- and it's an absolute blast. You might as well give it a try. If you don't like it, you can always go back to hunter.
Good luck and have LOTS of fun!