Blimey. How long is a piece of string?
Depends what you wanna do, how accurately you wanna do it, and how long you want it to last.
If you just want to do basic automotive diagnostics, then something that'll read AC and DC Volts Amps and Ohms will do. Pretty much any digital multimeter will be accurate enough. If it's likely to get nicked out of your workshop, get a cheap one.
Something I find most useful is an audible beeper for continuity testing, so you don't have to look at the meter.
A meter with a diode test facility is handy for checking rectifiers, etc.
I happen to have a Jaycar catalogue in front of me. You can get a Digitech meter with all of the above from Jaycar for $17. It'll probably do all you need and last for years. But if it goes tits-up in 6 months, or gets run over, it's no great loss.
As you go up in price, you get more facilities like auto-ranging (which I don't find particularly useful, but that's a personal preference) and perhaps a capacitance scale. A frequency scale might be useful as a tacho. Some meters are designed for special functions and have confusing scales like hFE, NCV, etc. They're for electronics nerds who wanna test transistors and stuff. If you're just doing basic electrrics, steer clear of those.
If you wanna splash out more than $17 at Jaycar. They have a nice neat little meter (item # QM1323) for $50 that has all the basic scales, plus Capacitance, Temperature and Frequency. It's auto ranging, has a backlit display and continuity beeper. It also comes in a zip-up pouch to keep all the probe cables together.
Spend $100 (Jaycar catalogue # QM1549) and you can get all of the above and more in a tougher IP67 enclosure, data memory and a bunch of other trick stuff.
Generally, the more money you pay, the better protection you get against stuff like voltage and current spikes.
Go higher up the price range and you can get wireless USB or Bluetooth connectivity. Fuck knows why you'd want that though.
However, as Terry implied with his comprehensive answer, a professional electrician probably wouldn't be caught dead with a cheap(ish) meter from Jaycar. The industry standard for those guys is Fluke. They're quality instruments, tough, reliable, accurate and idiot-proof. But you won't get much change out of $200 for a Fluke multimeter with just the basic functions.