So, company has $5m to buy shares and has 5.7m shares on...

So, company has $5m to buy shares and has 5.7m shares on issue.

If they were able to buy $5m at an average of $25 it means 200,000 shares would be cancelled, or 3.5% of the total shares on issue, leaving about 5.5m shares on issue

If they buy $5m at an average of $50 it means only 100,000 shares would be cancelled or 1.8%, leaving 5.6m shares

If the share price reaches $100 and they buy $5m of shares at $100, only 50,000 would be cancelled or 0.9%, leaving 5.65m shares

Imo if an increase in price is the aim then a greater impact will be had not from trying to cancel the most shares but from increases in the actual share price.