Best thing to do is hard factory reset the device, you can download apps that remove virus but some don't always work.
If you have important pictures on the device you can transfer them onto a computer with a cable, but considering your device may have a virus, make sure the computer your using had virus protection enabled.
To reset, Their should be a small hole, pin size, located either on the side or the rear, maybe under the back case of the device.
After a factory reset the device should be free of infestation of any kind.
As for the cracked screen, prices vary, depending on who fixes it, could be somewhere from $75-250USD. All depending on how old the Tablet is too.
Goodluck, if you need any help. @mayer is amazing and can assist you. :)