as the client, i would always split the project into 2 parts - a functional spec and a technical spec. my job was to interpret and write the func spec as a kind of pseudo-code version of what i thought could be built. then i would commission a fixed price job of interpreting the func spec and re-writing it as a technical spec ie, click a button and take the user to a summary of xyz turns into a bit of SQL. the tech spec must be written so that any programmer could use it to understand what needed to be done. then I'd ask for a fixed price quote to deliver on the assumption that i could get multiple quotes if needed.
the benefit is that my coder who wrote the tech spec should be very comfortable with what is needed and i get to sell a lower risk $$ to my managers.
i doubt this is worth much but i've been in a similar situation and this is how i dealt with it:
1. try thinking about your life in 5 yr chunks - a steady paycheck to pay off my mortgage really fast (secure future) and manageable/flexible work hours to maximise time building a foundation for life with my little one before she turns 10 is a wise but dull way to spend a few years. knowing it's worth it, and why, may help with the grind.
2. find a minimum $$ number you can live with and then find the smallest company/association/NFP that will pay this. small companies may not need you to go deep, but they _love_ people that can go wide. make sure flexibility in time/location are agreed up front - see 1. Go wide in the weirdest way you can think of every single time ie, become their economics guru by focusing on the data visualisation first, not the SQL queries. refuse to use a spreadsheet at work. write reports in html and distribute as a package. organise an industry conference and grow it. seriously, you'd be surprised how much lattitude you can get if you actively pick to work for people that _want/need_ initiative.
3. understand stakeholders and how they influence the decisions your boss will make. see 1 and 2. try and frame every proposal as something that is both interesting to you and as something that will make your boss look good. build trust. be aware of being taken advantage of but remember 99% of people are reasonable so don't be too paranoid. creating and launching things is a habit not something you choose to do on a whim.
4. don't sweat the small stuff. it's just $$ - enjoy what you can and treat it as a process. understand where you're going, not where you are.
5. personal sanity - build or invest in something that can't be (easily) hacked by software. this is moat between your future business and the leech competitors. personal relationships are in this category as are delivery chains or quality>quantity. design and distribute a small range of programmable toys - partner with your local high school and build the reputation first etc etc...
6. look behind you occasionally. if you're not careful, you only look at the people ahead of you and how much more successful/rich/pretty/talented they are - considering how much of this is due to dumb luck, this will only make you depressed. stop occasionally and turn around - there are vast numbers of people around the world thinking exactly the same @#$@#$ thing about you.
7. again with the little ones. because it's important and you don't get a do-over. don't let their childhood memories be 'mum/dad was always busy' - when they're 12ish, they will barely want to be in the same room with you anyway ;-)
8. be with your partner - they're with you for a reason, make sure you don't just assume that will always be the case.
i think the hirers forgot that they are also being interviewed. not one of them seemed to feel that they needed to do anything other than allow the anointed one through the front door.
that being said, it seems as though each person selects people based on a wide range of criteria - i think the portfolio idea is probably the best, especially if other good programmers say they're good. Q is doing open source work the equivalent of building a portfolio with the benefit of allowing other programmers to rate your stuff?