Learn me: some kinda laser line contraption.

I'm looking to project a beam of light on my car so I can mask off some ultra straight lines for paint. This is on a Miata, so plenty of weird curves (thinking about masking a straight line on a bar of soap). 
 

looking for a cheap way to do this. None of that $140 laser line level things from dewalt or Milwaukee. 

Rent a laser level?  

https://www.amazon.com/Laserland-Generator-Alignment-Locator-Lighting/dp/B00UCMXLXE/ref=asc_df_B00UCMXLXE/?tag=hyprod-20&linkCode=df0&hvadid=312167686300&hvpos=1o4&hvnetw=g&hvrand=8104185724394821137&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9033178&hvtargid=pla-568175219466&psc=1&tag=&ref=&adgrpid=63813710042&hvpone=&hvptwo=&hvadid=312167686300&hvpos=1o4&hvnetw=g&hvrand=8104185724394821137&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9033178&hvtargid=pla-568175219466

just found this. 

Clear plastic tube with one end fixed/clamped at the level you want with water in the tube up to that mark. Move the other end around and wait for the water stop moving and make the mark on the car.

In reply to John Welsh :

Is that the kinda tool I want for this job? I mean, a level would be nice, since I can then clock my angles to ensure the stay the same. 

In reply to RossD :

I'm gonna need a more thorough explanation. Pretend I'm 12. 

Jump to the 3:10 mark.

Habitat For Humanity. I scored a really nice pro grade laser level with a full size tripod for $30 :)

But if you don't need to use it in broad daylight, I've found this little guy pretty useful. I've used it for aligning things on the ceiling, and aiming at the car from the side would suit your needs. 

https://www.amazon.com/gp/product/B075KJ954Z 

I'd probably measure up from the floor or the sill and put a pair of reference marks on the side of the car, then use the laser to connect the dots.