In this housing market I would come into it with as little cash as you can and would strongly discourage you against borrowing $ from a family member because this can turn into a shit sandwich in a hurry.
If you rely on the lion's share of your income from commission, I would go back over the term of your employment and look at what the average income is. I would then look at your worst month and use it as kind of a go/no go point and would base my price range around worst case scenario, not best.
This is coming from a guy who has been self-employed for more than ten years and has had his share of ups and downs. In a situation where you eat what you kill, it can be chicken one day feathers the next and it's not always what you think can happen that does and leaves you spinning.
Also, foreclosures are a much quicker close than a short sale. I actually recently short sold a house and bought another short sale. It's a huge convoluted story but the house we bought had a second on it and you would not believe some of the stupidity we went through. The house was literally 3 weeks from full foreclosure which meant the 2nd mortgage would then have no claim and they still tried to play hardball with us over a couple grand. The ink was literally dry, we were going to close and I got a call at 11 in the morning (2 hours before close) that the 2nd and 1st were arguing over the HUD. The good news was it actually saved me 3 grand on the purchase price because they asked us to come to closing with more cash in hand and we told them no. Ended up negotiating it in our favor.
If you have the time, I would tell you to watch a property you like, see if it goes foreclosure and then swoop in. The reality of things is you will get a home with no warranty but often times they are sold with cash back to the buyer.
Short sales are a hassle and they blow up all the time. Pick half a dozen properties you like and hope a deal falls through and grab it as a foreclosure. It will save you a lot of head ache, IMO.