Diving is not for the tight wallets. You will get solid gear and instruction for about 1500-2000 out the door best guess. This will get you wet with own gear. After that you may find things you upgrade, areas you get into that require more gear and/or more instruction. It is a little more for start up than other hobbies/sports/activities, but after you get the gear, you will find it is not so bad long haul. Eg snowboarding down here (I noticed you are in SoCal) would run you at least $150 a day for gas, lift ticket, food at the resort. Golfing would run you ~$30-100 in green fees, etc. Once you have your own gear, and if you join a dive club, you will meet people quickly. Getting out to Casino Point for a weekend may run you $75 for the day - 2-4 dives, 6am to 3pm or so.
So it is all relative I suppose...