Let me know when you find a low cost 7" tablet with 300 ppi. You're going to be looking for a while. Don't confuse what you need with a Kindle e-ink reader and what is necessary on a 7" tablet.
For a small tablet, over 200 is fine. The top of the line $1,200 iPad Pro doesn't even have 300 ppi.
The newest iPad mini will support that ppi, bring your wallet. You can get the iPad mini 4, which has 324 ppi, for about $300.
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