Have you considered trading-in your existing iPad? You can verify eligibility for trade-in and obtain an estimate of the potential trade-in value here:
Apple Trade In - Apple
You should be able to trade-in at a physical Apple Store or online - many choosing to trade-in at physical store as the device can be checked, the trade-in value finalised and the process completed while in-store. Be aware that Apple’s in-store trade-in values may differ slightly from the on-line estimate.
Alternatively, consider selling privately - and use the proceeds towards the cost of purchasing a new or certified refurbished recent model iPad from Apple or an authorised Apple retailer. Refurbished models are indistinguishable from new, have a limited warranty, and are often attractively priced:
Certified Refurbished Products - Apple
Before parting with your iPad, whether trading-in or selling privately, ensure that the device is properly prepared:
What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support