MAKING YOUR OWN SYRUP
There are premixed syrups available for sale on several sites including Soda Club and Prairie Moon.
I prefer to mix my own syrups.
I purchase concentrated soft drink flavorings from Prairie Moon Beverage Company in 4oz 120mL bottles.
I sweeten my soda with Generic Aspartame (Equal or Nutrasweet). You can use almost any kind of sweetener that you prefer. I've never used sugar, so I'll provide a link to Prairie Moon Beverage Companies Recipe Page.
Prairie Moon syrups can also be used to flavor coffees, ice cream, and in mixed drinks.
Prairie Moon offers 41 flavors of concentrated syrup flavorings. I'll include a list of these flavors on the last step. They are continuously adding new flavors to try out (they also drop the most unpopular - they can't all be hits).
They are sold in 4oz 120mL bottles. Although you can buy individual bottles of syrup concentrate, the price is reduced for larger orders. Order 24 bottles and the price is only $2.49 per bottle. You can pick any variety of flavors for the order. You could purchase 24 different flavors in that single order. The choice is up to you.
I ordered 12 bottles in an assortment of flavors with doubles of my favorites. Since it was my first order I didn't want to do the full 24 until I'd tasted them. Now I'd have no problem ordering 24. These flavorings are DELICIOUS. I can also mix them with my favorite sweetener and to the strength that I choose.
BIG NOTE ABOUT MEASUREMENTS AND COSTSThere are huge possibilities for cost differences. I like a lightly flavored, lightly sweetened, highly carbonated soda. If you like a different style your costs and measurements will be different.
Costs change drastically with quantity also. I can only tell you what it costs for me.
*I rounded all Metric conversions to what I think is probably the common size used.
* * For example the 4oz bottle of concentrate actually contains 118mL. I used 120mL for the calculations.
* * A single serving in the U.S. is 16oz, that is 473mL. I used 450mL for the single serving conversion as I think that is the standard size used in many countries.
Please let me know if you find a large error. Small mismatches in conversions are probably because of the simplification of measures.