This is a difficult question because everyone has different spending habits.  Spending falls into the following categories:

Meals on Sunday.  You will get three meals a day, Friday through Saturday, but you are on your own for Sunday.  It's possible to get by on 5 or 6 bucks a day.  For instance, a quarter of a roast chicken with fries costs about $3.00 in Huanchaco; a menu (the daily special) can be as little as 4 bucks.  A fancier meal is about 5 bucks, and a steak or seafood dinner will run you about 10 bucks.

Laundry.  There are good laundry services in Huanchaco.  They charge by the kilo.  About 5 to 15 bucks a week should cover you unless you go through a lot of cloths.

Snacks, soft drinks, beer, etc.  This varies a great deal from person to person.  A cold coke at a restaurant costs about 40 cents, a 20-oz beer about a buck.  Bars and clubs charge about the same.  At grocery stores (bodegas) you pay somewhat less.  Snacks are cheap.  We supply all your drinking water.

Email.  Internet cafes charge about 40 cents per hour.

Transportation to and from Trujillo.  Taxi to Trujillo from Huanchaco is about 4 bucks for the whole car (not per person), 30 cents for the bus.

Gifts and Souvenirs.  Impossible to say.  Crafts such as sweaters, jewelry, and pottery are cheap.  There are plenty of opportunities to shop in Huanchaco and Trujillo.  For a hundred bucks you can get a lot.  A good copy of a Moche pot runs 10 to 20 bucks, small pots and figurines cost a few bucks, earrings or necklaces, a couple bucks each (excluding gold or silver), and cheap sweaters costs less than 20 bucks.

Other costs.  If you are staying over night in Lima, a cab from the airport will cost 20 bucks.  A night at a cheap hotel in a good part of Lima will cost around at least 25 to 40 bucks for single.  Surfing lessons in Huanchaco are about 10 bucks for a half day.  You can hire a Spanish language tutor for about 5 bucks.  An American movie, with Spanish subtitles, costs about 2 or 3 bucks in Trujillo.  Cigarettes are cheap, very cheap if you get them at the duty free shop at the Lima airport (right before the baggage claim).  Marlboros and Lucky Strikes are the only foreign brands available in Trujillo.