How much is DEX worth?

If it is within your financial power, you can, of course, by a DEX as there is no harm in doing so. Although you may spend a significant amount of money if the DEX in question has no established userbase. There are hundreds if not thousands of DEXs already so the highest by net profit are those established DEXs like Uniswap which just cross the trillion-dollar mark in transactions. The blockchain where the DEX was built can also affect your business. Ethereum is the most popular blockchain for DApps, and large exchanges like Curve, Convex, SushuSwap, and Uniswap are all on Ethereum.