I've trained both at home and at gyms. At home, with a bench press w/adjustable uprights, a few hundred pounds in weight, and a couple stall mats, the cost in total is around $500. The cost of gym membership, free - unless you count school tuition.
Between the several locations, I'll always perfer training at home where anything goes and a lack of equipment does not hinder me. Within the next year I also plan on scrapping most of what I have for a new set of squat stands and a few hundred pounds of bumper plates. Price tag of about 1,200... but will be worth the expense.
The most expensive piece that does collect dust in my garage is my set of dumbbells which go from 15lb-70lbs. A few will be used on occasion, but have served primary as a place to hold my water bottle, hang my belt from, and let my sweaty knee sleeves dry off. I've also 150lbs worth of dumbbells at the base of my pull up/dip "station" which have not been moved in a few years. It doesn't hurt to much though... I have them if I ever need them and much of that weight was given to me in exchange for a cheap meal at a local pub.