Budgeting Your Money
No one can order you not to purchase something. They can counsel you, recommend you attend budgeting class, etc. but they cannot tell you how to spend your money.
You might consider the following: put together a budget, go to your unit NCO that helps Soldiers with budgeting. If one is not available go to ACS and request their assistance.
Once you have a solid budget with a little flex for emergencies you can consider purchasing the vehicle.
Next, while the NCO you mentioned might be looking out for you it is also possible the care you buy could be a lemon. So it is very important that you make sure the care is good to go. Have a mechanic check it out. If it is a new care it comes with a warranty so you should have no problems.
With regard to your BAS, there is usually an option that will allow you to have the money taken out over a period of 12 months. Check with finance
You might want to see your PSG and PLT LDR on open door policy and provide them some insight as to what is going on. You should be careful how you handle this event.
You might also be interested in the following post: