10K works out to $120k a year, that is about normal for a salaried senior level developer. Given that salary usually denotes 40 hr a week, 2 weeks vacation, sick leave, a portion of taxes paid and 401k matching. If any of those are not in the mix you have to reduce the compensation by that amount to come up with what it equates to in salary. if it is W-9 or 1099 that is about $80-$90k in compensation still at the bottom end of a senior developers salary. Developers naturally assume that there will be crunch times of 60-80 hours per week but if those kind of hours are the norm 10k is pretty low. I work in constant crunch of at least 60-80 hrs per week and my weekly earnings are slightly below the same as that monthly amount my monthly earning are around 3X that amount. I do corp to corp W-9, and I have a rare skill set but ruby developers are not exactly falling out of the trees either. 10K sounds about right to me, it is nothing spectacular and a ruby developer should be able to find that from a variety of potential employers. That said, you should expect normal working hours for that amount if they are a salaried developer, if they are contract you should expect around 30-35 hours a week.

10k @ 40 hrs per week is $62.50 an hour - if this is a short term contract it's not that good. Even as a longer term contract it isn't that great. If it's W9 it's even worse. If it's 1099 it's a little better, but still not going to get you top talent. My pulse on the current market for rails developer's isn't that current, but I'm guessing you'll need to get closer to $100 to $120 per hour to find talent at the higher end of the spectrum.

You should not worry about hours. You should worry about results produced over months (or even quarters). Whether the wage ends up being $50/hr or $250/hr matters little so long whatever you need done gets done on time.

Caveat emptor: I'm a developer.

Is there a correlation between "quality of work" and "hours [...] put in"?

As a contractor I'd do productive work for around 100 hours per month.

As a full-time employee I'd be in the office for 160 hours and probably do productive work for around 80 hours per month.