We would recommend getting the 5th Generation iPad minimum to ensure you continue to get software updates.
Buying a number of new tablets upfront can total a large cost. Here are some alternatives to buying you can consider.
Using a authorised reseller such as Hardsoft, ensures you are getting a quality device at a reasonable cost for your business. Leasing prices start at around £2 per week for older models and most offer the option to own the device at the end of the lease period. Check out some websites below:
Looking for second hand devices can often cut a considerable amount of the cost. However, this does carry some risks such as little/no warranty, possible damages & no return options. If you do choose this route, here are some sites you can trust.