Here is a link from IDEAFit that lists certifications by the category you choose. (IDEAFit is not the certifying agency–they are all individual and have their own costs) I believe this link is by cost, but you may want to also consider other factors such as whether it is NCCA accredited (holds more merit) and the clientele you will be training.
Also, here is an older article but you can see the importance of choosing a good cert…. Best wishes.
You might also check with your employer for their preferences on a certifying agency. Some are fine with a less-prestigious but well-respected agency with current information and qualified instructors; some employers will only accept certifications from specific agencies. You might also check if your employer will assist with tuition, or you could work out a plan where some of your hours normally paid to you go toward your tuition. Good luck in your fitness endeavors!
I can understand a need to keep your expenses down. Especially in the early stages of your profession. But I recommend that your education be second in your business expenses only to your business overhead expenses. It is investing in you to get as much education as you can. I am fortunate to find educational growth almost as enjoyable as my physical workouts. Time wise, I put in at least four hours a week for studying. And that doesn’t include time spent on researching material for specific client issues. The best advice I can give anyone is to make a career in a field that you would spend hours on for free if it wasn’t your career. If you don’t want to study your career subject, maybe it isn’t the right career for you. Not that I am accusing anyone of not being passionate about what they do, but there are many people working in jobs they hate. How could someone just do that day after day and not do something about?