One tip: The petticoat goes a long way and makes ANY summer skirt or dress look amazing!! Take this check dress in the right image from Topshop. It looks AMAZING with the petticoat underneath.
Not really as inspiring....
I recommend hunting around some charity shops for some really good value ones as they will be much cheaper than anything you will find in a Vintage shop. However if you're not a charity shop digger then Beyond Retro is an obvious, yet no hassle choice.