This may seem like a stupid question, but I have a slow leak in my 1995 Mazda Protege's transmission fluid tank. What does something like this cost to get fixed, and in order to replace the fluid do I place it where the transmission fluid dipstick is, because I can't locate a tank to save my life. Thanks.

Yep: you are absolutely right. The only way to add ATF is to pour it down the dip-stick tube. A cheap plastic funnel and a bit of time and it's relatively painless!
Make sure everything is spotlessly clean though!

The transmission fluid can be leaking from the pan gasket, or from one of the axle seals. Depending on where the leak is located, it may cost anywhere from $ 100 (for transmission pan gasket, filter, and fluid replacement), to about $ 300 to fix (if they have to pull axles to replace the axle seals). You may also have a leaking transmission dipstick tube O ring.

Take a look at your power steering fluid level. I believe that Mazda uses tranny fluid in the power steering system. The problem may be your steering rack , not your transmission.