Apple does offer the facility to return an undamaged/unwanted item within 14-days of its original purchase from Apple. By your description, you are well beyond the 14-day cutoff - and as such the opportunity to return and exchange your iPad has been lost.
Apple's trade-in programme does not accept current-models. As such, until your iPad is superseded, trade-in won't be an option. When trade-in does become an option, the potential value will be significantly less than you paid.
As such, selling your unwanted iPad privately will likely be the only way to recover a significant proportion of the purchase cost - which you can put towards the purchase of a Mac computer.