Transmission fluid type problems

[ShortRoundChief]

So I started to go to class today and my car wouldn't shift. After further inspection it was bone dry and apparently I had a leak that I put off. Well I can't put it off any longer.

My questions are: It turns out that these things have transmission filters that need to be replaced every 30k miles. I didn't know that so needless to say it's due. I'm unable to do it myself so I need to take it to a mechanic. How much does that normally cost and could the lack of proper maintenance have caused the leak?

I appreciate the insight and will promptly die in an AIDS fire .