All I can tell you is that PMI is such a tiny thing to consider. As Jamie suggested, lenders will give you a loan that won't exceed 80% on the 1st mortgage and then they'll drop a 2nd mortgage behind it for the full 20% if need be. This will eliminate the PMI or Private Mortgage Insurance factor.
Really, there are many banks that will loan 100% even in one loan without PMI. I know this because I have worked in mortgages the past 3 yrs
I'm all about leverage, so the way I would do this is this- (over simplified version)
EXAMPLE: Subject property is appraised at fair market value for $200,000
I would write an offer for $180,000, seller to pay 3-6% for closing costs (or state a dollar amount- $10,000).
Then, I would get a loan for 100% financing, with no prepay (if I must do a prepayment penalty, 1yr is fine).
Essentially, what I've just done was bought a piece of property with no money down, seller paid all of my closing costs and after the loan funds, I will have a property with $20,000 in equity.
Sure, your payment will be higher then that of your rent (depending on what type of mortgage you're in), but you'll get pride of ownership and you'll be on your way to building wealth, should you continue to expound on that.
Call it going to the next level.
If your property appreciates 10% in the next year or so, you now have $40,000 in equity. 10% the following year and you've got around $65k. Follow me here?
Appreciates higher than that, then fuggetaboutit......