This is possible, especially with 20% down. The real catch is what your expectations are for that home. The inventory in Rancho Penasquitos at that price is often distressed, older, and needing updates.
As to whether to use your wife or another Realtor - that's a personal decision. I will pay a referral fee when working with a licensed Realtor. You are likely to be dealing with short sales or foreclosures in this price that garner multiple offers. There are some tricks of the trade your wife may or may not have learned in winning a multiple bid scenario.
Feel free to contact me should you wish to discuss this!