What kind of light meter are you looking for? Because if you want a spot meter, then a Soligor Digital Spot Sensor is probably your cheapest option (on a good one). If you're looking for an incident meter, do you need flash capabilities? There are quite a few good options here, but I'd probably avoid any selenium meters. I have a few, and while they work, they are not accurate (but they are consistent so I can use them provided I know how far off they are).
If you're looking for a reflective meter, which I assume is the case since you're talking about something that goes into the shoe mount, then you're not going to be able to do better than a good phone app when it comes to accuracy (unless you want to use a full on DSLR for your meter). The thing with reflective meters is most don't tell you what they're metering off of. You simply point it in a direction and it picks up whatever and gives you a number. It doesn't tell you how it's weighing what objects, nor does it give you a good idea of what is included and what is not in it's calculations. A phone app will show you all of that on it's screen, so it's much more accurate for taking measurements than a regular reflective meter. So if it's giving you a reading that will actually blow out your highlights due to your subject being a dark color, you'll see that on the screen. The fact that they happen to be much cheaper (sometimes free) is a nice addition too! Plus, it's one less thing to carry, since you probably were going to be carrying it anyway.
So if you need a spot or incident meter, then you might need a new meter. But if you want a reflective meter or matrix meter, then you need a new app.