Define “ipad alternative”.
IPads, windows tablets and android tablets all have different “feel”, apps and usage.
Generally, tablets can be compared in the same screen sizes, then processing power, then build quality.
Multiple chinese tablets exist with the same 4:3, 9.7″ screen as the ipads, this may be a good starting point.
Windows and android tablets come in all sizes and screen ratio, so you would need to see what your usage is.
Some examples of tablets with that same screen:
Teclast X98 Plus II
Onda V919 Air CH