Mille Fleur is not inexpensive but their lunch is an excellent value for money when you consider the impeccable ingredients and the skilled preparation. Their patio has a pleasant ambience. The wine selection is outstanding and the service is attentive and thoughtful. It's less than two miles from Chino Farm.
You're in Rancho Santa Fe so nothing is all that cheap there. You can get out of Thyme in the Ranch (which is very, very good) for about $25 for 2 people. There are a couple of coffee shops in the area as well. Another option is to jump on Via de la Valle and just head in towards the race track or towards Solana Beach- your options get much better there.
In the other direction is Loic which is very good as well, but around the same price point as Thyme in the Ranch and a bit further away.
I've never seen a halfway decent food truck in Rancho Santa Fe