RESTAURANTS : RESTAURANT REVIEW : A Big Catch : Oversized roadhouse has a large menu of Mexican seafood and other specialties from south of the border at up-market prices.

Supply and demand, we’re taught, is the first rule of economics. How else could you explain the fact that La Paz, a Mexican seafood house in Calabasas, gets away with charging $21.95 for a huge bowlful of caldo de siete mares , the Mexican equivalent of bouillabaisse?

Perhaps this objection is slightly unfair. No one I know objects too strenuously to the idea of paying $21.95 for bouillabaisse itself, because we accept the idea of up-market prices for anything with a French label on it.

But though this soup is impressive, loaded as it is with shrimp, fish, abalone, crab legs and clams still in the shell, it pales when compared with more soulful versions of siete mares available in Boyle Heights or Santa Ana. And let’s face it--if this oversized roadhouse were in East Los Angeles, the dish would be around half the price it is here. (The menu also lists a simple fish soup--sort of a poor man’s siete mares-- made with humble halibut at $11.95.)

La Paz in Calabasas (there is a second La Paz in Woodland Hills) is a free-standing stone building with an enormous lofted ceiling--pasted up with dollar bills, of all things--and an ambience best described as cheerfully impersonal. Seating is at big square tables with green plastic tops. The wooden chairs are the carved, high-backed kind for sale in Mexican furniture shops from Tijuana to the Guatemalan border.

The menu is appropriately big, as well. Soups and succulent seafoods abound. There are caldo de camaron , loaded with shrimp, and campechana , a mouth-watering combination of shrimp, abalone and octopus, and, of course, a selection of seafood cocteles --shrimp, oyster or abalone, shelled and marinated in tomatoes, onions and cilantro and served in cocktail glasses.

La Paz puts a premium on freshness. The restaurant buys fish fresh several times a week and prepares it in a variety of ways. For example, Mexican perch ( mojarra ) offers quite a few options to the adventurer; you can get it a la plancha (grilled), empanizado (breaded), al mojo (fried with garlic) or a la Veracruzana (with tomato sauce).

Instead, someone at my table opted for the specialty of the house, whole rock cod, Yucatan style. This is a gigantic fish colored bright red from a spicy rub of achiote , served on a gleaming metal platter with pinkish pickled onions, good black beans and mushy Mexican rice. I’d rate it adequate, though I’ve had far better.

That would also be true for one of the specials I’ve had, paella ole . If you bear in mind that this classic Valencian seafood and rice dish easily serves two, the $19.95 price tag goes down a lot easier. Just get a load of the components--crab legs, shrimp, an entire lobster tail, fish, clams and grainy, pungent bits of chorizo sausage. It almost stirs up the blood. Too bad the rice--the basis of the dish--is as mushy as the rice that accompanies all main dishes.

Should you hanker for non-seafood items, there is an entire page of them on this menu. Tacos stuffed with goat ( chivo ) or chicken ( pollo ) are available, as well enchilada-type standards. Chiles rellenos come in a sour cream sauce.

Chicken mole has the traditional chocolate-based sauce, but it’s heavily thickened with sesame seeds, halfway to a pipian and somehow twice as filling. Barbecued goat ( birria de chivo ) is more like it. High marks for the soft, stewed goat meat in an aromatic sauce made from ginger, beer, chocolate and cinnamon. It has an authentic flavor many of the seafood dishes seem to be missing.

The achiote of the Yucatan-style rock cod also surfaces in carne asada Yucatan style and poc chuc , a Mayan pork steak. Both meats are rubbed with the ground seed, also known as annatto , and then grilled. Go for the pork, cooked up in little pieces with a good deal of lemon and garlic.

Given this restaurant’s pricey dinner structure, it comes as a surprise to find an almost unbeatable bargain at lunchtime, namely a huge express buffet at only $5.99. Now you get to make your (chicken, beef or fish) fajitas, tacos, burritos, enchiladas and tostadas, and flank them with good plain boiled beans a la olla , salad and fine, cumin-spiked albondigas soup. Just don’t expect them to throw in the Seven Seas, not for this price, anyway.

WHERE AND WHEN

Location: La Paz, 4505 Las Virgenes Road, Calabasas.

Suggested Dishes: lunch buffet, $5.99; barbecued goat, $11.95; chicken mole , $11.95; shrimp soup, $15.95; campechana , $16.75.

Hours: Lunch 11 a.m. to 2 p.m. Monday through Saturday; dinner 2 to 9 p.m. Monday through Thursday, 2 to 10 p.m. Friday and Saturday, 2:30 to 9 p.m. Sunday; brunch Sunday, 10 a.m. to 2:30 p.m.

Price: Dinner for two, $25 to $55. Full bar. Parking lot. American Express, MasterCard and Visa.

Call: (818) 880-8076.