The only real cost will be the CO2 if you use a small system as mentioned above by the 'Green Flash' but my nano has no CO2 and has excellent growth from the Aqua Soil, but there are some plants that will not grow well without CO2, other than that costs are minimal.
I didn't use all of the ADA soil amendments but I would like to try them as you seen the amazing difference in the link mentioned earlier, his root mass is just unbelievable using all the ADA substrate goodies and it's only $136 over the cost of a plain setup.
My nano is all of the shelf items like, a stock 2.5 gallon Aqueon tank that I cleaned up nicely with just an Exacto knife, a Red Sea nano filter, a UP Aqua UA-F17 LED (this is my only piece of hight tech gear), Aqua Soil, plants and shrimp. The whole thing cost me $247.08 and out of that I have spent $90.04 on shrimp and shipping as I killed the first 2 batches of shrimp I bought, but the tank has no heater or thermometer,no fertilizers or Excel has ever been used and the shrimp are breeding well.
The one thing I can say about a nano setup is it is much harder that a larger setup, my tanks have always been large and with a large volume of water you can absorb mistakes without any casualties but with a nano a small mistake adding ferts, Excel, or just a small ammonia spike can wipe out your live stock. I only feed my shrimp every other day and a tiny amount in a feeding dish so I can remove the excess, I change 1 quart of water weekly, and I alternate cleaning my filter intake sponge or filter media every other week with a water temperature around 70 degrees so I won't kill the bacteria (these tanks have very little area for beneficial bacteria and this is where those substrate additives can really help) and when I do the filter media I always add a fresh 1/8 teaspoon of activated carbon, this routine has paid off with a lot of Tangerine Tiger offspring!
Good luck and consider trying a low tech nano as you can always add CO2 anytime and if you click on the 2.5 gallon shrimp nano in my signature line you can see the growth I've had over the last couple of months has filled the tank without CO2.