Automotive is typically going to be low frequency stuff, at least if you're looking at things like crank/cam/distributor position sensors, injector pulses, etc. I don't think I have ever used a scope while working on a laptop, the signals in modern computers tend to be well up into the GHz and lots of differential signalling, it's the sort of thing requiring exotic and very expensive instruments to measure.
$100 is going to limit you to what is effectively a toy, although one of the little Chinese pocket scope gadgets might be useful for the sort of automotive sensor signals I mentioned above. Looking at sold items on ebay it looks like you can occasionally find one of the older Fluke Scopemeter handhelds for under $300, other options are the inexpensive hobbyist aimed scopes like the popular Rigol and Siglent models which while not handheld are quite compact, you're looking at close to $400 for those though.
Oscilloscopes are and always have been expensive instruments, and while they are an order of magnitude cheaper today than they were 30 years ago they are still not exactly cheap. It's one of those things where you can pick any two characteristics, useful, cheap, compact, can't have all three.