I do not claim absolute objectivity, but I will suggest what I would buy precisely for the car’s diagnostic needs.
If the aim is only the identification of the signal, you can choose:

a. simple kits, which can be purchased on eBay, for example:

b. handheld oscilloscopes, for example:

c. cheapest USB oscilloscopes, for example:

d. cheapest table oscilloscopes, for example:

All these oscilloscopes are characterized by:
a. memory depth: small, typically till 4K points;
b. waveforms/sec – not specified.
These two key properties for me is enough to make a conclusion – none of these oscilloscopes is worth buying. Regardless, it costs 20 EUR or 200 EUR.
With such an oscilloscope, you will not see the sporadic problems. You will lose a lot of time, and saved 100 .. 200 EUR will not pay off.

Entry-level oscilloscope. Which one to buy? Several examples

a. Pico Scope 2206B or better (prices, starting from 299 EUR)

b. Micsig TO1000 (prices, starting from 399 EUR)

c. Rigol DS1000E/Z series or better (prices, starting from 299/349 EUR)

d. Siglent SDS1000 series (prices starting from 299 EUR)

e. Lecroy T3DSO1000 series (prices starting from 399 EUR)

f. Owon XDS2000 series (prices starting from 319 EUR)

All these examples are characterized by a Memory depth of at least 1M points. Increasing the budget for 50 EUR, Memory depth increases (typically) till at least 12 .. 24M points.
For the cheapest (on the list) oscilloscopes, the Waveforms/sec is not indicated, but the memory buffer of a solid size ensures that even if the glitch is not noticed in the real-time mode, it can be identified when checking the recordings of the data.
I do not particularly highlight the sample rate and the signal band because even for the weakest examples, these parameters are more than enough for automotive use.
It is possible that someone will oppose – this oscilloscope has additional math functions, this – built-in generator, this – wider band, but this – wider possibilities of the memory access. Yes, the objections are in place, but I doubt that someone in the range of automotive diagnostics will calculate the sensor parameter values; will use the generator; will enjoy the 100MHz band instead of the 50MHz band, etc. In this entry, I am talking about the first serious diagnostics tool, which can be used to learn to work with it.

Unfortunately, oscilloscopes of the following brands failed the first selection:
a. Keysight – noticeably more expensive, additionally 1000 series has a memory depth of around 200K points;
b. Rohde & Schwarz oscilloscopes are noticeably more expensive than the indicted budget (299 .. 399 EUR);
c. Hantek – this manufacturer did not indicate the Memory depth and waveforms/sec parameters on his webpage for the entry-level USB oscilloscopes;
d. UNI-T – limited technical information, limited purchase possibilities. The impression that this company actually only repacks the oscilloscopes developed by other Chinese manufacturers.