It is claimed the La Liga outfit want the 22-year-old for the remainder of the campaign, with a view to signing him permanently in the summer.
However, Everton are only interested in a permanent deal and have set the asking price at £8million in the hope of making a quick profit on the £5.2million they paid last summer.
Everton have set the price that high despite the fact Sandro has struggled to adapt to life in England, scoring just one goal in 15 appearances.
The valuation looks sure to scare off Betis and Everton may have to rethink their valuation if they wish to recoup some cash on the Spain Under-21 international.
Theo Walcott is set to arrive from Arsenal in a £20million deal and after also signing Cenk Tosun for £25million, boss Sam Allardyce needs to balance the books.