Evans claimed his Sky Bet League One club had a bid for May rejected, although St Johnstone denied reports late last week that any official offer had been received.
Evans told BBC Radio Sheffield: "We offered £300,000 and were quoted £800,000. That price is out of our range.
"We left our offer on the table and asked them to get back to us and they haven't, so I have to assume they value him at that amount.
"People in football are only worth what people are willing to pay and St Johnstone are entitled to price him up as they see fit.
"He has got a lot of attributes that I like and he's scored consistently over the last three seasons."
The 21-year-old has scored 11 goals this season after netting 45 times in 57 games during loan spells with Alloa and Hamilton.
The Scotland Under-21 international, who was the subject of a failed bid by Peterborough in August, last month signed a contract extension that ties him to St Johnstone until the end of next season.
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