Compared to an average US city, I expect you to find Belgium a very expensive country. Taxi's are extremely expensive, expect to pay >25Euro's for innercity trips. Having said that, public transport like trains and busses are really really cheap. The Belgian Railways have a card called Go Pass (<26)
or Rail Pass which makes traveling through Belgium rather cheap.
Since I am local to Belgium, I am not a good reference on cost of accommodation. If you are traveling in a group, you might consider going for self catering accomodation. Also check booking.com, which is a service that worked for me in many European cities. They often have very interesting offers on the day itself.
On food the choices are huge.
"Frieten" or French Fries start just below 2 Euro. Being a local dish Belgians consider part of their local heritage I would recommend to at least once visit a local "Frituur".
Other cheap options are going to the restaurants in the shopping malls, especially from the chains, but don't expect anything special there. Another cheap "fastfood" solution can be found in the many kebab places.
Then there are the all you can eat places. Almost every city or bigger village does have a "wokchinees", or a chinees restaurant where you can eat as much as you can for around 25-30 euro's. A different cuisine, but also all you can eat can be found at the Colmar (Link in French and Dutch only).
In general I would say that a decent restaurant dinner would start at costing you 20 Euro's per person. Be aware that in Belgium you pay for the water you order. There are exceptions (I am not affiliated), but in general a glass of water will start at 1-1.5 Euro's. You don't get tapwater, although in Belgium tapwater is of high quality.
Take home dishes (Pizza or kebab) will start around 5 euro.
If you are in Belgium in the Summer try to locate a local cultural festival like the one running in Antwerp: "Zomer van Antwerpen" with its zomerbar. Usually these festivals aim at a local audience (hence the Dutch only websites), but sometimes you can find some really nice dishes there for very decent prices and the atmosphere is usually brilliant.
The best advise I can give is to go outside the tourist centers to find a decent dish for a decent price. This also fits Brussels.