I have a planted 220 gallon tank. I actually have a dirted tank which alot of people don't do. I used organic soil, many use Miracle grow organic soil. Then I topped the soil with eco-complete. Organic soil is pretty cheap, Eco-complete is about $25 a bag, unless you can find it for sale (that is a 20 pound bag). Other people can chime in about what substrate they use and cost. The reason I went with a dirted tank is... I have had ponds from about 300 to 2000+ for about 15 years. One thing I learned is that when I had to grow plants in pots to put in the ponds, the plants I potted in soil always grew better, looked better, and flowered better. So after alot of research on using dirt as a substrate in aquariums I decided it would give me the results of plant growth I wanted. Organic soil is rich in nutrients but it must be capped with sand, gravel, something. Plant growth for me has been incredible without CO2
. I do use flourish excel for carbon. The cost is what you make it.... things cost but depending on the size of the tank and the equipment you decide to use it doesn't have to break the bank. Check Craigs List. You could do a low light tank with plants like Java ferns, anubia, bolbitus (african fern), and such which wouldn't require an expensive light system or even a fancy substrate. Plants are going to cost but many you can propagate and you can fill in areas over time. Do some research and you might be pleasantly surprized. Hope this helps.