If you stay in Tokyo more than one month, it is definitely worth while.
If you stay there for a week, it is not, at least in terms of saving.
Nevertheless, I assure you that you can have totally different experiences in Tokyo with your bike from those of a tourist only using public transportation.
You are freer.
To buy a second hand bicycle is not at all difficult.
You have various bike shops in Asakusa area. They often sell second hand bikes as well as new ones.
To sell one is another story.
Most of bike shops and second hand shops buy only expensive bikes, which you might not want to buy.
To sell your bicycle, you have to ride it to another district and return to your hotel by train.
Their selling price is between 5,000 yen and 10,000 yen. They don't disclose the buying price.
I will write an article about it now.
By the way, I just got a phone call from my collaborator Chi-chi in Thailand. He will be back in Japan a few day's time. He has taken more than 400 photos there and it is enough to launch another site.
He said, "A prodigious American site manager thinks that you don't have to have many accesses in one site. All you have to do is 1,000 sites with 10 accesses a day".