Battery voltage issue

[heckerp1]

Hello, I am currently working on making a rc hotwheels car using arduino and nrf24l01+ module. I will be using a servo motor's board as esc for the back gear and a 3.7g servo motor for the front steering system. the front servo requires anywhere between 4.8-7.2v while the back servo board(which im using as esc) requires anywhere between 4.8 to 6v. The NRF24L01is a general 3.3v one(pcb antenna). I am stuck in:

1. Deciding the board. I tried using arduino nano, but it is just a tad too big for this project. I cant seem to decide between the 2 pro mini (3.3v and 5v one ). Would also welcome suggestions for other arduino boards.
2. Deciding the battery. The available batteries are of 3.7v ones, so i would need to either connect them in series or use a step up converter. Even if i connect them in series, i would need to regulate the voltage from 7.4v to 6(or 5)V. Would welcome some help regarding this

Some additional info:

1. Cost is also an issue with me, as im limited to 10 dollars (for the board and battery combined)
2. The size needs to be small as its going to be fitted inside a hotwheels car(road bandit)
3. The servo motor used in making the esc is a generic tower pro model 9g

[hammy]

You might be better off looking for more voltage compatible devices , or where you can get by with only one voltage conversion .

If you only have $10 for this ( school project ?) , you might struggle and have to be more inventive ( eg not use servos ?)

Have good look at your spec and have a look at really cheap RC cars/toys

[hammy]

3.7 volt servo

[heckerp1]

This one is available, but it costs more than my budget itself

[heckerp1]

What would you recommend for the battery?

[hammy]

Is this a school project ?

If so it maybe designed to make you come up with new ideas to achieve the budget , such as not using conventional servos .
You need to research stuff and look at other concepts