My family is planing to go to to Florida for vacation this summer. And I want to go scuba diving, but my mom wants to know how much it would cost? Any ideas?

If you aren’t a certified diver and want to go off exploring on your own with a buddy ( even if they are certified), you’re outta luck. Not happening.
That said, some resorts or dive shops local to resorts do offer a sort of guided tour. They’re called, naturally, resort courses and take about half a day. You’ll be taught basic skills and use of equipment and be taken on a guided tour of a local shallow water dive site with a Dive Master or above accompanying you.
How much? Depends on the dive shop or resort. You don’t mention where you’ll be in Florida and it’s a big state. Cost can also vary with the number of people the tour has. Private tour will be more bucks.
Your best bet is to search for dive shops and resorts in the area you are planning on going to and fire off an email to them asking if they provide a resort course.
One thing I should mention here. You will NOT become a certified diver by going on one of these tours. It won’t even count towards a credit to taking an actual Open Water course. You will get a better bang for your buck if you actually do the full Open Water course academics at least, at a dive shop local to you. You could then have the actual dive portion of the course transferred to a dive shop at your Florida destination. PADI offers this service. You’ll study, do your pool dives and take your exams at your home location, the dive shop will arrange for the open water dive portion to be done at a shop close to your destination. Once you’ve done your open water dives in Florida, you’ll be a certified diver and you and a certified buddy can go off diving or you can get on a charter as lone walk on and they’ll buddy you up. The cost for an Open water cert are anywhere from 200-350 bucks. It all depends on supply and demand. You’re pretty well at a dive shop’s mercy there if they are the only game in town. More shops…more competition and you’ll get a better price.
The alternative is to do your entire course where you live ( including the open water dives) but if you’re at a place where there’s ice and snow…you ain’t gonna be doing those open water dives now.