I am shopping for an audio signal injector/tracer and would like to know what you guys recommend or prefer. I'm finding lots of kits and DIY circuit designs online as well as vintage test sets on eBay. I would prefer a readymade purpose-built device, but I'm not averse to building something either.

Thanks!

All you need is an audio tone generator, computer speakers to act as your tracer, and a simple diode detector circuit (if you want to trace RF/IF signals with modulation).

Check on Ebay and see what they have there. Ive got an Eico 147 signal tracer that I picked up a few years back for $30 to replace one that was so well-used the selector switches were worn out. The 147 traces RF, AF, and has a test speaker, test amp, wattmeter functionality, and even a test speaker function with built-in output transformer. All in all, a handy piece of test equipment.

I also have the solid state version, the Eico 150. It works well, but I prefer the more robust tube-based 147 model.

Check on Ebay and see what they have there. Ive got an Eico 147 signal tracer that I picked up a few years back for $30 to replace one that was so well-used the selector switches were worn out. The 147 traces RF, AF, and has a test speaker, test amp, wattmeter functionality, and even a test speaker function with built-in output transformer. All in all, a handy piece of test equipment.

I also have the solid state version, the Eico 150. It works well, but I prefer the more robust tube-based 147 model.
I bought my first signal tracer in 1963. It's an Allied Knight-Kit. I bought it to troubleshoot transistor radios. It's about the same as the competitive makes with the test speaker, output transformer, watt meter ETC.
Allied always used new production components instead of the war surplus parts like Eico and Heath used. :D

I picked up a Knight kit tracer for free a few months ago, and gave it to a friend. It had all the same features as the Eico, just different case styling. I've had some very good Knight kit equipment in the past, but they're not as plentiful as Eico.

All kit test equipment, regardless of brand, is only as good as the person who originally built it.