First on cost. For the World Cup they have probably tripled or quadrupled. For everything.
Safety issues are, you are find if you don't act like a dumb shit tourist. Keep money and valuables out of sight. Don't wear expensive watches and stuff. Don't carry an expensive camera around your neck. During the day it is fine to walk anywhere but at night take a taxi everywhere. In Rio for hobbying go to a terma. Lots more fun with a great selection of girls. My favorite is Centaruous but I hear that Monte Carlo has really picked up since the closing of L'Uomo. Downtown 4 x 4 is the king. Not every taxi driver knows where everything is but all taxi drivers know where Centaruous is. Just get in and tell them "Centaruous". Note also if that if you really click with a girl at a terma she will gladly give you her number and come over when she is off either before or after her shift. Escort agencies are find but the issue is finding one that speaks English. My suggestion is to join
www.clubhombre.com and read the trip reports and find B'Wana Dick's Guide To Rio that is on that site.