Where can I find a pair of Duffle bags ?

Anywhere from Walmart, to Target, to your local sporting goods store, to a luggage store, to a place like Lands End.

How basic or how fancy?

If you want really ugly but really strong canvas duffels, go to an Army-navy surplus store. They sell the real thing. Ugly but will last forever.

But you can find designer duffels at lots of other places.

Large, simple and cheap.

REI duffle

Eddie Bauer, Timberland,

Costco has bags for $10 a bag. They are insulated. You need a $55 membership fee.

My answer will depend on what exactly it is you want to put in them…........