For me, it has been about $150 a month.

Nearly EVERY hobby can suck up a lot of money. That's why they don't have hobbies in other countries. No time or no money. Or both.

RC planes have fewer moving parts, but when they crash, it is usually pretty bad.

Motorcycle riding requires not only the multi-thousand dollar motorcycle, but also tires, ($300 a year) a helmet, ($400 every five years) a jacket, ($200 every 10 years) boots, gloves, pants ($200 every 10 years), gas (that is the real killer; it isn't $12 a gallon like nitro fuel, but they burn a lot more.) The bright side is that they're useful transportation as well as fun. On the other hand, it is hard to get killed doing RC, and easy in motorcycling.

Photography is expensive. Printing costs a lot, as does traveling to new places to photograph. Photography is another useful hobby though. The initial outlay is quite easily over $1000 for a good camera and two lenses.

I don't know how you nitro guys do it. Nitro will just nickel and dime you to death. Brushless motors last pretty much forever, but I guess the batteries don't.

My wife knits. You wouldn't believe how much a serious knitter can spend on yarn. The good stuff costs $13 a skein (ball) and it takes a minimum of 3 skeins to make anything. At least you have to (or should) finish the project before making something else.

I also do woodworking: The initial outlay for tools is tremendous, but they do last for many years if you buy quality stuff. Plan on about $2000 to get started. The nightstands I built required just over $300 worth of lumber, (Ash) but it took me 2 months to build them, so that was pretty cheap. However, the electricity bill went up about $60 a month.