Well, you're going to pay for four years of college regardless of what you do in high school. The college will just pad out your schedule with more required courses.
I doubt this is true for many schools that give credit for AP exams. I studied computer engineering. My AP exams got me credit for introductory programming, freshman chemistry, and four of my five humanities electives. That let me graduate a semester early. This is not to say that every AP exam you take will help you graduate earlier, even at colleges that award credit for AP exams. By the time I had to sign up for AP exams my senior year I already knew which college I would be attending. I looked and discovered that two of the exams for AP classes I was taking (English Literature and Statistics) would count for credit but would not help me fulfill any additional degree requirements for any of the majors I was considering at the time. So I saved a bit of money and time studying by skipping those exams.
For me, getting a master's turned out to be a great decision career-wise. But I would say it depends a great deal on the specifics of your situation. Here's mine:
I graduated with a BS in computer engineering from a middle-of-the-road university. I had a decent job offer coming out of college, but not with a company I wanted to work for in the long term. I was accepted to a master's program in computer science at a top tier university, and decided to do that instead. I'm going to graduate with my MS next week.
I believe just being at a better university has opened doors for me. Last summer I was able to score an internship at a company that probably would not have given me a second look if I was an undergrad at my previous school. Now I have an offer to work as a full-time software engineer with another great company.
My pay will be slightly higher than my undergrad friends at this school who are going to that same company, but probably no higher than theirs will be after two years of experience there. If I had spent two years working at the company that gave me an offer after undergrad, would I have been able to get this same job? Maybe, maybe not. I do know that my initial salary with this company will be nearly 50% higher than the other company offered me two years ago.
In your situation, you have to consider what value will be added by going for another degree. What work opportunities are available to you now? What new opportunities will open up as a result of your master's education? How much will a master's degree cost, both in terms of tuition and lost earning potential from being out of the workforce during that time? These are all things you need to consider. There is no easy, cookie-cutter answer.
10.0 times 0.1 is hardly ever 1.0.