Extract isn't cheaper than grain. You don't need a lot of hops for a wheat beer, but you need some. I guess you already have a pot? If you want to go cheap, get whatever grain your recipe calls for, a BIAB bag (about $10) and a 5 gallon round cooler from Walmart (about $20). You can add a spigot (another $20-30?) or be cheap and skip that. Mash in the cooler, pull the bag/grains out, put bag/grains in kettle that has heated sparge water in it. Dunk, stir or otherwise agitate the bag/grain, then pull the bag/grains out again. Pour the wort that's in the cooler into the kettle, and you're ready to boil. You can add equipment and fine tune your process later. Have some wheat extract on hand in case you don't hit your numbers.
There's a lot of steps/details I left out, so ask any questions you may have.....
Where to buy? Buying online may be cheaper than your local homebrew store, maybe not. First stop should be HBT sponsors, many have great prices and service.