Under £20 for this 8BitDo wireless gamepad - compatible with SNES mini and NES mini - for £19.96 delivered including VAT.
Not sure it works with a Switch as it isn't Bluetooth compatible, but maybe you could play it wired via the USB.
SN30 2.4G Includes
SN30 2.4G Controller
2.4G Wireless Receiver
- Brand Name: 8Bitdo
- Compatible Brand/Model: Nintendo
- Nintendo Model: NES
- Certification: CE
- Origin: CN(Origin)
- Package: Yes
- Type: Gamepads
- Model Number: 81BA
- Interface Type: USB
- System Compatibility: SNES Classic Edition & SFC Classic Edition
- Connectivity 1: 2.4G Wireless Technology for SNES/SFC Classic Edition.
- Connectivity 2: USB connection for Windows, macOS, Raspberry Pi, Android and more.
- Special Features 1: 2.4G Receiver powers directly from the SNES/SFC Classic Edition.
- Special Features 2: Access the SNES/SFC Classic Edition HOME menu wirelessly
- Package: 8Bitdo SN30 2.4G/SF30 2.4G Controller,2.4G Wireless Receiver,USB Cable