Aloha and welcome back to the awesome world of scuba! To answer your question about how much you might be spending...well, that depends upon a lot of factors. Just like w/purchasing ski gear or gear for other sports, you can start by spending $1000 for a complete set up or $4000 and anywhere in between.
I am a fan of renting gear at least a few times so you can experiment a bit but it sounds like you prefer to start off buying your gear outright. If so, I agree w/DiverBizz that you should start at the mid-level and go up. Buying cheap gear just doesn't pay off and you won't be satisfied. I once had an instructor who kept buying cheap gear and it was embarrassing how often it kept breaking on him.
If you are planning on diving the Caribbean on a regular basis, you can tailor your gear to that end...if you are going to be packing your dive gear, you'll want to look at the lighter-weight, travel-type bcds. A good reg set up w/regular gauges will start around $500 or so, a good computer anywhere from $500-1000, a good, light wetsuit for the Caribbean will run at least $100, throw in mask/snorkel/fins for approx. $200 and you are already in for $1300 - $1800 per person. No need to buy a tank although you might want to have your own weights if you are going to be diving at your vacation cottage.
I am a HUGE fan on working w/your local dive shop on your gear, as long as you can find someone who will genuinely help you and help you tailor your purchases to your needs and not their bottom line. Sure, you can find deals on the internet but if this is going to be a long-term sport for you and your son, you'll want to build a great working relationship with the people who will be training you, helping you, and diving with you.
Hope this info helps. There are other great threads on what to look for in a good local dive shop (lds) and/or in a good instructor. Happy diving to you!