What are the costs to consider when making jam?
Costs to consider when making jam: 

One-Time Costs


Pressure canner  
Water-bath canner  
Large pot for making jam in  
Strainer (can use a colander-type item or something like a Squeez-o)  
Jar rack that goes inside the canner  
Jar lifter  
Funnel  
Jars
Freezer-safe containers  
Jar rings 


Recurring Costs


Jar lids
Fruit (you can often get pretty cheap fruit in bulk from an orchard)
Pectin 
Sugar 
Spices 
Energy usage (stove)


Compare costs for freezer jam (no canner required), pressure-canned jam (pressure canners are expensive), and water-bath canned jam. Also compare for recipes that do vs do not contain pectin.

If you can get a lot of the one-time cost items free (from grandma's attic, most likely), and if you can get the recurring cost items on sale (or from your own garden), then you can probably come close to commercially priced jam. 

Personally, here's what I look at:
A) The cost of the item I would normally buy at the store - generic, cheap brand. Let's call that price X.
B) The cost of the item I wish I could buy at the store - the really good stuff. That price is usually about 2x to 3x.
Then, my goal is to be cheaper than 2x.  

Another Cost Consideration
If you give homemade jam as holiday gifts, spending less than you otherwise would on a gift, there's additional savings for you.