I pay less than £2.00 a pair for my safety specs from Cromwell and usually buy 10 at a time. They have a lanyard to hang round your neck. I haven't bought any for some time now as I try to take good care of them.
These are my rules:-
1) Never put them on a bench. Always hang them by the lanyard.
2) Never rub the "glass" with fingers or rags.
3) If they need cleaning always use warm soapy water with minimal rubbing, Rinse and leave to dry or use compressed air if in a hurry.
4) When they get scruffy throw them in the bin.
All very obvious but it took a long time before I realised that I needed to be very strict about this.
Having looked through some very murky safety specs I often wonder how many accidents are caused by people who can't see what they are doing.
Regards.
David.