Well, It depends what you are looking for in the system. Their is a 3G/Wifi Model, and a Wifi model. Retail price for the 3G/Wifi model is around $299.99 and for the Wifi model, The price ranges around $249.99. Theres various bundles like the Call of Duty: Black Ops Declassified bundle and the Assasins Creed III Liberation bundle which each are about the same at the Wifi model which is a good deal because its the same as the wifi model and you get a game and a memory card at the same price. Although they have the Ps Vita Instant Game Collection bundle which is an extremely good deal because for $299.99 you get: 4 games which are Uncharted Golden Abyss, WipEout 2048, Gravity Rush, and Unit 13. It also comes with 1 free year of Playstation Plus. Last the vita system which is a 3G/Wifi model so you get 4 free games, 1 year of PSPlus, and a 3G/Wifi Vita system. New bundles are soon to come like The Walking Dead. Hope this helped guys!
I believe the cheapest place to buy or get a PS Vita would be Amazon since they are also very reliable in their services. However you can still check out eBay and see if you can get it at a cheaper price.