I also have to agree, a sixteen year old that put A LOT of thought and effort into a tattoo CLAP CLAP CLAP! I think you will be pleased and happy with choosing a tattoo that has meaning and will be with you forever. You are definitely mature for your age which is nice to see for a change on here.
I also agree. I would like to see more people answering questions on here that are actually in the areas they want to be in. Why are you answering questions about tattoos if you hate them and are repulsed by them etc, etc. Go to another area and answer questions I am sure this nice girl does not want to hear your opinion about how much you do not like tattoos, etc, etc.
Now as far as cost goes for a medium tattoo with color I believe that has pretty much been covered here pretty well. A lot of things are going to depend on your location and what not, so I agree it will probably be anywhere from $120 to $160ish depending on where you go. But the only way you are going to know for sure is to ask around about reputable shops that preferably deal with custom work and then go into the shop and talk with one of their artist and explain to him/her what you want. They will give you a rough estimate of cost. At that point you will know for sue how much you are looking at for sure.
As far as healing time goes it usually takes a max time of two weeks for a tattoo to heal, the roughest patch is the first week when all the pealing and what not is taking place. Just make sure that you follow the artist specific instructions for taking care of your work. Always make sure that you use sunscreen when you are in the sun, as this will keep the colors very bright and prevent you from having to have touchup work done as often.
As far as making your idea any better, I don't think there is much I could add, It sounds great already! Good luck with your first bit of work. Only obstacle I see is getting past your age, hopefully you can get work done with parental consent good luck!!