Years ago I had a planted 150g community tank and it was cheaper and easier to upkeep than my nano reefs I have now. The set-up for anything is what costs the most money. But you already have most of the equipment. As far as maintance, on my 150g planted tank, all I remember doing is monthly pruning and filter cleaning. I never did any water changes (I was lazy) and don't recall how frequently I dosed the tank with fertz. Of course I had to feed the fish twice a day, but that is easy. Only problem was the plants grew fast and I couldn't count all the fish I had... I don't recall what lighting I had, but replacing the bulb never broke my bank. I never dosed co2 back then neither since I didn't know about it. There are many plants that are easy to care for... so the work depends on the difficulty of the plants or their sensitivity.