I wish that we had the kind of income where I could call photography my "cheapest hobby" - as it is, to get this kind of money invested in upgrading, I had to tell hubby (and this is an honest intention on my part) that I want to earn money with this going forward. This is at this point a business investment, though the sole purpose of the business end is to invest more money in my kit until I have every lens and body I want.
As a "hobby" photography and music are probably neck-in-neck. I own a spinet piano, a higher end Yahama Clavinova, a $1000 Yamaha portable full-size keyboard, and an Alvarez guitar... (oh, and a classic wooden clarinet from the 1950s and a 1920s vintage silver tenor saxophone). Writing as a hobby is only at about $700, so definitely a far, far third. Now, if you count my chicken raising a hobby it costs me about $90/month, cost me $800 for building stuff, and about $80/year in new stock. I've been at it for just over two years now... so I guess it would be between writing and music.... ?
I really need better hobbies... crocheting - pfeh - it has cost me less than $300 total including all the stuff I've crocheted and given as gifts! ROFL
the hobby that really gets me is the 4 cars in the garage totaling over 500k. it's easy for me to justify spending on photog gear, keeps me from buying another car. Before anyone asks, I yank teeth for a living.