How to economically make home-made sushi?
Sushi does not require fish, sushi is the style of rice preparation (rice, salt, a little rice vinegar, occasionally some kombu). So long as you have the correct preparation of rice, you technically have some form of sushi (you could just throw it in a bowl with some additions on top and have a type of sushi called chirashizushi).

Second, there is no such thing as sushi grade fish - sushi grade literally means the fish has been frozen for over 24 hours to kill any parasites present. Otherwise, just about any clean fish can be used (as always, fresher is better). 

As for sushi making, you can use any number of ingredients to make it, you don't specifically need fish. In fact, if you are trying to throw a sushi party or are just hungry for some rolls, this may be a better way to go since you can use what is on hand. Here are some ideas:


Canned eel
a fried egg
a filet of salmon (again, freeze it for 24 hours and then thaw)
Carrot
sweet potato 
cucumber
avocado
imitation crab or crab
shrimp
tilapia
lox
cream cheese
squid


When you make it yourself you open up to lots of possibilities and chances to experiment. Since you are looking to do this on an individual level, play around a bit. If you have your heart set on using fish, talk to a good seafood counter and get small portions of fish. If it is 100% fresh, kill clean and store for 24-36 hours in a freezer, then thaw and use. Don't buy in to "sushi grade" fish because it is pure marketing.