Condition on eBay probably doesn't mean much. Most people really don't know the difference.
Any time you purchase 2 or more try to haggle. Pricing is usually based on single purchases.
Record local/online stores know what stuff is worth so are best for titles you don't think you will find elsewhere.
The best scores I've found come from estate sales.
Goodwill, SA, etc. gets good stuff almost daily. It is picked through by the end of the day.
Like electronics, the more often you stop and look, the more likely you are to find something you like.
Clean vinyl and clean sleeves are not necessarily together, but paying $1 each for 2 to make a good set is cheaper than $10 for both clean in a single purchase.
If you offer $5-$10 for a whole box of records at a yard sale you will probably go home with them.