I agree with the 2 previous posts, take a breath and slow down. If you invest $4000 and for any reason don't complete then what? Even if you save a few hundred.
You have your OW, and AOW, you are still enthusiastic, go and enjoy a some dives with a buddy (no instructor). Plan and execute those dives yourself, gain the experience.
Spend some time diving, Do not get "hung up" taking course after course, you are not collecting pretty cards, you are going to get real diving experience.
Often schools will bundle courses together to save you money, just do not buy too many at once and only do the ones you are interested in.
Do not choose your dive school on price, some large schools turn out DM and instructors by the score, anyone who drops out, drops out and is money gained (for them). You will need good tuition and lots of support to become an Instructor, this is more important to you than the cost in $$$. Once you have your Rescue Diver a good school should allow you to assist with classes a couple of times before you sign up for the DM course. A lot of schools find their new staff members from the students they bring along, so they should have an interest in what sort of DM you are going to be.
You also need lots of diving experience, away from the instructors. You need to be more than comfortable in the water, you need confidence and the experience to "understand what you don't know"
Lets look at Padi courses for a typical student.
Open Water 4 dives
Advanced open water 5 dives
Rescue diver 4 dives
Along the way they may do say, A Nitrox course, (2 dives usually), A drysuit course (if from colder climates) and Peak performance Bouyancy (which lots of schools offer as a special price add on to OW).
That's a total of 19 dives, all under supervision and you only need 20 dives to enter the Divemaster course.
So you are taking the big first step to being a Dive Professional and actually what diving have you done? yes you have the dive requirements, but what experience do you actually have?
I have had DM students who have taken this route, paid a lot of money upfront and then really struggled with the reality of assisting new divers and having the confidence to be an effective Divemaster. They would be the first to "drop out" because the enthusiam has been drained from them because the DM course is the first time they have had to think for themselves. I used to counsel them to put the course "on hold" go and do some diving and then restart the course.
Please do not let any of this put you off your ambition of being a scuba instructor. I am just saying there is much more to it than paying out $4,000 and taking a load of courses. Hard to say whether that is a good or a bad price though, it all depends on what is included in it. Padi course materials cost are a large investment for both DM and Instructors. Others will comment on other agency costs.
I wish you the best in your ambition, there is very little in this world more satisfying than taking people underwater for the first time.
T