My numbers are rough estimates and your mileage may vary. That much said:
A basic scuba certification is going to cost you the better part of $300 plus the cost of the 4 required OW dives.
You will ultimately find that if you dive fairly regularly, purchasing your own gear makes more sense than renting, especially for local diving since you aren't going to be concerned with packing it on an airplane.
A good set of used gear can be had for around $1000, and some of that you will have to purchase anyway, your "personal gear" which includes mask, fins, and snorkel. I compare used gear to rentals because the stuff you rent isn't close to new.
Some rough numbers
Mask/fins/snorkel $150
BCD $200
Wet suit $150
Booties and gloves $40
Single AL80 $100
Weights $20
Dive light $30
Regulator $100
Gauges $200
If you had to rent the gear (other than mask, fins, snorkel), it's going to cost you at least $40 for the day, so somewhere around 20 dives is the break even.
Once you have a basic gear configuration, filling a tank for a local dive will cost you about $5 each time. The only other expenses will be gas to get to your local dive site and any entrance fees. A yearly visual is required which is around $20 or so, and a "hydro" (more detailed tank test) is necessary about every 5 yrs and is a few bucks more. Regulators should be serviced annually, cost is about $50-70.