Here’s an affordable digital piano, with usb connection. Alesis Recital | 88 Key Beginner Digital Piano / Keyboard with Full Size Semi Weighted Keys, Power Supply, Built In Speakers and 5 Premium Voices (Amazon Exclusive) https://www.amazon.com/dp/B01DZXE9NC/ref=cm_sw_r_cp_api_i_hPAfFbMMBW66W

Here is the cable you would use for iPad.

MeloAudio USB 2.0 Cable Type B to Midi Cable OTG Cable Compatible with iOS Devices to Midi Controller, Electronic Music Instrument, Midi Keyboard, Recording Audio Interface, USB Microphone, 5FT https://www.amazon.com/dp/B07FLWN6G4/ref=cm_sw_r_cp_api_i_QWAfFbR33XVME

Now you just need to find your DAW on the iPad!

Maybe too obvious to be a hack but a USB Type B to Lightning cable allows you to connect to your iphone or ipad and record using garage band or similar directly out of the amp.