Ah yes, the hidden downside of sound -- once you get one, you'll want 'em all to have it... I actually have found the much-maligned MRC Sound Decoder to be a great option here. Costs 25% of the higher-end sound decoders and 40-50% of their "bargain" versions (e.g. Soundtraxx "LC" series)... Yet, to my ear the sound quality is about 75% of the top end and pretty close to the 'bargain' level ones.
Sure, I have high-end sound decoders in my high-end locos which I tend to run more frequently anyhow. But with a motive power roster of 16, 10 of which have no sound as of yet, I'm looking at spending $2,000+ to do the remaining ones "high end" and $600 to do them "good enough"...
Bottom line, at $60 a pop, you can sound-equip a lot more locos and lot more quickly than you can at $120-$200+ per...
Kris