It Depends; What networks are you looking to accept? Are you a registered business and willing to undergo KYB checks for AML purposes (This typically only applies to gateways that have a fiat offramp feature/are licensed)?
For Bitcoin check out BTCPayServer (0% Fee), it's self hosted. I'm quite a fan of NOWPayments (0.5% Fee) as it possibly has the largest number of payment methods out of all the options. Coinbase Commerce is quite popular in the Blackhat community (1% Fee)
There's no shortage of good options out there, just search and find one that meets your needs.
Also what e-commerce platform are you using? Check what plugins are available, otherwise you'd need to hire a developer to use the gateways API.