If you have no problems with your electricity rate then it is a good offer relatively as you have to deal with the fact that Rx 580 is produced in Summer of 2016 and they have been used for quite some years.If these are not an obstacle for you than 300 Mhsh is a good hash rate for a 2500 USD price offer.
RX 500 series was an updated Polaris version if the RX 400 series released in spring 2017.
https://en.m.wikipedia.org/wiki/Radeon_RX_500_seriesIMO, you are better off with the newly released RX6600 XT. Same hash rate as the RX 580 at 40% less power and a 3-year warranty vs a 4 year old GPU run hard in a Chinese warehouse. Those fans will probably be shot. Better resale with the newer cards and GPU availability has already started to improve and it will will improve more the closer the expected ETH POS merge date nears.