Good sushi is very good, but bad sushi can be nasty. Depending on where you live you can probably find decent quality sushi at a reasonable price. Your best bet is to ask people you know that are already sushi fans for the best reasonably priced place to get sushi in your area. If you like avocado a California Roll would be good to try first. If not, I would suggest a Spicy Tuna Roll.
Sushi and sashimi are fish and seafood with rice or seaweed, respectively. Try the popular ones like California roll or salmon roll. If the sushi is fresh --really fresh and recently rolled---it doesn't taste or smell fishy. You have to acquire a taste for things like this--just like raw oysters, called "shooters".