I use exel for all my financial stuff. And I use a couple of formulas to calculate how much I can spend on certain stuff. At the moment my budget for lego is 15% of my income. Due to some job switching lately, it can vary from €50,- to €150,- a month.
You could also buy all the needed bricks from BL and/or PAB. It will be much cheaper.
That's what I'm doing right now with the Market Street, it will cost me around 100 euro's in stead of 180 euro's.
And there is no motor, so you'll have to rely on brute handtwistingforce to raise and lower the crane due to the LA's.
But it isprobably easy to add PF to the model.