It is best to work with a Realtor when purchasing new or existing homes, so they can aid you in negotiations and refer you in the right direction for a solid ethical lender, that right there can save you money. I recently had to stand up to a lender (a buyer chose) for over charging my client, and other things. Ethical lenders are out there.
Remember it is a declining buyers market in AV and sellers need to participate in aiding the buyer to get their home sold, if they don't another seller will, this is where an agent can assist you in YOUR best interest. Keep your thoughts open to learn and team up with an agent. Keep an eye on mortgage interest rates, that certainly can cost you money. Lots of great buys in AV, live like a king in the great aircraft/aerospace cities!
If you wait for the market to turn around, you may loose some of the incentive for sellers to provide such assistance.
As for the other methods, sweat equity is th added value of any labor you put into improving a home you already own, and builder incentives typically are not the kind of things that equate into an increase in the DP.
If your reason for asking this is to reduce the time during which you will be paying PMI, pay a little extra on the mortgage each month and track the appreciation rates after the market recovers. When you reach that 20% equity mark, you can request that the PMI be dropped.