It seems Digitrax is the only company that trully surves the 8 pin plug-n-play market and they have sound option for fairly cheap proubly due to being around for awhile, costs do get cheaper over time in electronics.
In the last year or two I've picked up quite a few of the recently discontinued / upgraded MRC sound decoders for very good prices - usually around $35-45. They come with limited horn selection, but if (like me) you have a lot of first-generation EMD and Alco diesels that use a "BLAT" single chime airhorn, they work out very well.
I am very interested in the responses you will get because I'm in the same boat. At some point, MRC was the "cheapest" option for sound, but in my experience, quality has been a bit unpredictable. I installed some 10 years ago that are still running strong, while more 2 recent installs (5 years ago) fried on me for no obvious reason. I'm not even sure they will make them again, so this might be a moot point.
I think the current cheapest option is Digitrax, and I see that they still offer a low end steam-diesel decoder. Although the sound options are VERY limited, I find that the Digitrax decoders are rock solid. I still have a few steamers to convert - I will probably go that route the next time. I have too many engines to go for the high-end stuff. If I only had a handful of locos, I would definitely invest in Locksound... But the cost is there.
Simon
I've always used SoundTraxx decoders (1100, 2200, 4400). Sometimes friends will say these sound decoders are too expensive for their tastes, and they will ask me to recommend more affordable solutions. Can someone please recommend more affordable sound decoders in various sizes? It would be good to know "cheapest possible" as well as "mid level quality", so I could recommend a couple of options. Thanks.