I want to buy this ESC (https:/myhelis.com/HOBBYWING-SkyWalker-40A.html#product-details-tab-description), which i am GUESSING is from the skywalker v2 series. Does anyone know if it can reverse? I want it for an rc car. If not, can you recommend any esc (in the 15 - 20 euro budget, it is just for a school project) that can reverse?

Just look up the manual and read it:
HW-SM048DUL_Platinum-HV-300A-V4.1说明书(A2)-20180820 (hobbywing.com)

yeah, I did that, but "brake mode" isn't exactly going in reverse, isn't it? I don't know if the manufacturer meant "car reverse" when they said brake/reverse mode for an AIRPLANE esc.

edit: nvm I am blind
"After selected this option, the Reverse Brake signal wire (its signal range must be the same as the throttle range) must to be plugged into any vacant channel on the receiver, and you can control the motor direction via
that channel. The channel range of 0-50% is the default motor direction, and the channel range of 50% to 100% will cause the motor to spin counterclockwise. The channel stick should be within the channel range of
0-50% (0 would be better) when the first time you power on the ESC. After the Reverse function is activated, the motor will stop first and then spin in the reversed direction and then increase to the speed corresponding
to the throttle input. Either signal loss, no matter reverse brake signal loss or throttle signal loss during the flight, can cause the throttle signal loss protection to be activated."

This is probably not your best option for a car ESC. Not sure what other constraints you have (motor/battery etc), but there is another thread with a discussion on budget ESCs. The Hobbyking ones are generally cheap. Suitable for a lot of things, but not generally used by racers. For example, something like this: https://hobbyking.com/en_us/hobbykin...w-reverse.html

Some considerations to keep in mind:

• What battery are you using? Is it a LiPo? what voltage?
• What motor do you have? Is it brushed/brushless? If brushless, is it sensored? What size and turn specifications does it have?
• Car weight/size/gearing will all influence how it will perform, but I imagine for a school project, your objective is not a speed run