Ok, as you can see, there are a lot of biased people here. I'm not pointing fingers, but basically, you can see that people will generally recommend the treatment that worked for them. And who can blame them? If it worked for them, they obviously want others to benefit from it, and it's the only thing they know to recommend.
Here is my input:
Minoxidil: Use this if you want to continue applying it for the rest of your life. If you stop, you will most likely lose everything you've gained through this. You have to apply it twice daily, and in my personal opinion, it is a pain. It makes your hair feel weird, and gives it a weird texture and colour. (As you can see I am biased against minoxidil). Try it if you like. Buy one bottle, and apply it for a few weeks. If you can picture doing that same routine for as long as you want to keep your hair, stick with it. (Assuming it works).
Cost: Can be as cheap as a few hundred dollars a year.
Finasteride: Pop a pill once a day to slow or stop your hair loss. More side effects "possible" with this (compared to minoxidil). Best used for diffuse thinning, not great for bald areas. Think of it as thickening and strengthening your existing hairs. More "regrowth" with minoxidil. That said, finasteride has been known to provide regrowth too.
Cost: Proscar (split into 4th or 5th) can cost a few hundred a year.
Propecia: Around 50USD a month. Depending on where you get it (can be more or less I think).
dutasteride: Stronger than finasteride, therefore, better for your hair. More chances of side effects. I don't know that much about this one. I've heard it inhibits two types of DHT, as opposed to finasteride which inhibits one type.
Cost: No idea.