Rosa Mexicana is kind of like an upscale mexican chain. The margaritas are good! If you guys like Mexican food and strong drinks, you can also check out lauriol plaza, which is a 3 store mexican restaurant near the Adams Morgan neighborhood (if you walk straight up 18th street, you will hit it a little past R street).
DC prices are kind of like New York prices as far as food goes - not quite as bad, but getting there. Since you're staying near the White House, I would definitely check out Old Ebbit Grill, which has a huge menu ranging from burgers to upscale foods. It has a very "DC" feel to it.
You can also check out Georgetown. The waterfront is lovely this time of year (Georgetown harbor) and you can grab either the circulator bus or the georgetown shuttle or walk right in along Pennsylvania Avenue. These restaurants tend to be a little bit more upscale but again, each will also serve sandwiches, burgers, etc. I would check out the menu for Sequoia online. It is one of my favorites. Georgetown is also nice for walking around and upscale shopping.
If you are in the dupont circle area (around 20th and P to 14th and P), there are tons of restaurants. I live here and it's an easy walk to the White House. There are a couple of well known, inexpensive restaurants here - I love, love Meiwah for chinese food. Huge portions and very reasonable prices. It is right by my apartment and always packed. You can also check out City Lights of China, which is up a bit on the actual Dupont Circle, which continuously also wins cheap eats awards but I think Meiwah is far superior.
If you guys are in the mood for Italian, I would probably recommend Famous Luigi's at 19th and L for reasonably priced Italian, and..don't hate me for saying it, but I love Bertucci's (it's a chain, like olive garden but nicer) and they have a location inside the mall at 2000 Pennsylvania (white house is 16th and Penn) and also a location on Connecticut Ave a little bit more towards Dupont Circle.
You might also want to google because one of the top chef contestants opened up a burger place by Capitol Hill that is supposed to be reasonably priced and very good. If you'd like any more specific recs, PM or update the thread.