You can buy pure sucralose (the stuff in splenda) online for $10/ounce. It's around 600 times as sweet as sugar, so that's equivalent to paying about 25¢/lb of sugar.

The upsides are that there are no documented negative health effects, it tastes pretty much like sugar, and it has no calories.

The downsides are that it doesn't work like sugar chemically (you can't caramelize it or use it to activate yeast), and that you have to dilute it (I like to just make a very sweet sucralose+water solution to sweeten things with, but you could easily cut it with some other powder like maltodextrin).