How does one begin to create salsa?
Recipes
As far as salsa recipes go, they're all over the web. Check sites like allrecipes.com or epicurious.com - - or justrightmenus.com! 

Shelf Life   


Refrigerator. With regard to shelf life, according to stilltasty.com, you're only going to get 5-7 days out of fresh salsa in the refrigerator.
Freezer. The same source says you can keep it for 1-2 months in the freezer. Use containers meant for storing frozen foods (they make plastic lidded containers for this very purpose), and leave "headspace" in the container (room for expansion as the liquid freezes). If you opt for freezing, you can use any recipe you'd like. Food safety won't be an issue so much as quality would. For example, I would not recommend freezing a melon salsa, though it's great fresh. 
Canning. You also could pressure can your salsa. The National Center for Home Food Preservation is the best resource to learn to can. If you opt for canning, be sure to follow a trusted canning recipe - you can't just can any old recipe. I would use one off the National Center's site. 


Cost Comparison
It all depends on what you make and the price of your ingredients, of course. If I can get cheap salsa at cost X and expensive, tasty salsa and cost 2X, my goal in making my own is to achieve great taste at a cost less than 2X. My homemade blueberry jam costs me about $2 per jar, much more expensive than generic jam; however, good blueberry jam is about $5 at the store. 

Incidentally, I'll be making salsa this summer once I can get lots of cheap tomatoes. Keep an eye on jessica.mcrackan.com late in the summer if you'd like some real examples and cost comparisons.