Or in my case, suppose you bought a projector and then upgraded it for the new model after 200 hours....three times. I don't even want to think about the hourly cost in depreciation. Thankfully I'm happy with the latest one as it's approaching 150 hours now, I hope to keep this one a bit longer than the last.
As Kelvin says depreciation is the biggest cost to factor in running a pj.
If you are constantly craving for a better image you can spend thousands upgrading but if you are sensible and spend under £1000 and keep the machine till the bulb goes(hopefully 2000-3000hrs) it will have cost you 20p-30p per hr which will probably be over at least a 3-4 yr period.
What other fun can you have for that kind of money.