For me personally, i try to not do the cheap thing with everything anymore. Since you only need a small amount you can enjoy the rest as well. If you have a little money than your options are higher, if not than I am sure you can find something to work. Every time I say i am going to add something, I end up never stop tasting. Basically I like to splash the beers. Maybe a little more, maybe a little less. Maybe some red wine, maybe some white. In fact just racked a plain porter and this thread has inspired me to splash it with something. I wont go up to 50 for a bottle, but maybe something still nice. There are some really good small batch artesian groups in denver and my lq tasted all the barrells and picked one for the store. Point is thats how I want to spend my friday night, drinking some killer bourbon beer listening to records.
For full addition, get a friend or two together and measure small amounts at a time into a glass. From there calculate for full batch by taste, less is more and you can always make it stronger. Careful to not get to lit up. That math from calder seems rock solid.