I noticed that as well and started asking around. It turned out the $50 price tag was a glitch in the TI system. It seems it's been fixed now. At least the pricing on Mouser has been adjusted to something rather more reasonable.
Tom
We'd really need to see the feedback network of his preamp, as the 49720 might actually be lower noise than the 49990 in-circuit. The former has pretty darn low current noise (1.6pA/rtHz), while the latter doesn't (2.8pA/rtHz).
For BJT-input, though the OPA209 is going to be the winner for noise for most audio circuits (e.g. for Rf around 1k or so). Other opamps are clearly better for other reasons, though (just to be thorough).
I'd try the ADA4898 as a replacement for the 49990 though. Both are exquisitely high performing chips that require some know-how to get the most out of them. OPA211/OPA1611 is in barking distance, too.
(I wrote this to complement Monte's post, not in disagreement!)
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I tried the OPA1611 (TI suggestion) as a replacement for the 49990 but I didn't like the results. It turns out it's output stage is a current source and the OL gain varies with loading.
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