Transient Parking at SMO
If proximity to Van Nuys is #1 then Whiteman is probably a good choice.
At Santa Monica transient parking is $15/night and fuel is resonable (for the area) at the American Flyers self serve pump down at the approach end of runway 3 on the south west side. I have to admit I'm biased though, it's my home airport.
I can't comment on Whiteman since I've never been there, but I can say that avoiding Van Nuys is probably a good idea. Most of the FBO's there are geared towards the Jet Set. I'm sure fuel is pricey and you'll have to pay a "handling fee" as well as the overnight if you don't take on the minumum amount of fuel. I've never been to Van Nuys either but I'm basing this on my experiences flying into Santa Barbara. It's a great airport but it cost $$$ to stay there.
If you need any local knowledge or ideas for places to fly while you're done here don't hesitate to drop me a PM.