Its difficult to say...are you selling $5 items which are costing 30c per click with Adwords or are you selling $2000 sound systems that are costing $1.50per click?
I really wouldnt be worried about the budget or cost....normally i average around $30 per day for an ecommerce shop that i operate. But during the lead up to Christmas my budget increases to $100 per day. The fact is that i sell so much i really dont care about paying $100 per day for the simple reason being that every sale i make, makes me money
The important and utterly vital part of Adwords is to fine tune and target specifically what you are selling so that the clicks truly are made only by interested people. this is the art as it ensures the clicks arent wasted and costs are minimised
So....dont worry how high the budget goes as long as you are mainaing a good CTR and good conversions percentage.