If it was $31.. (not including shipping) then there's a good chance it might be close or over 50mW.
And if your happy, that's all that matters. :beer:
And 'harshing people's buzz' is in no way the intention most have. However We get several a day here who truly believe they can get a 'high power' green for $20 or less just because they can get high power reds for that, which in actuality it's just not possible due to the difference in how the lasers actually work and are manufactured. So the knowledge that 'cheap greens are rarely up to spec' is one of the things that we try to hammer into new peoples heads, heh.
$30 for a 50mW sounds about right though so it's possible it's 40mW+ of green. But the only real way to tell is with a LPM and an IR filter.