A Surface Pro 3 is an excellent choice in that it is a quality product that allows you to have a "laptop" (with type cover) and also the convenience of a tablet when you need it. Personally, I think they are overpriced somewhat but I'd jump at the chance to own one myself. If this is strictly a school device and you don't mind using external storage or relying almost exclusively on the cloud, the cheapest model with the i3 would serve you with no problems whatsoever.
The base i5 model is a fairly substantial jump in power for a moderate increase in price whilst also doubling your SSD size. The i5 model would allow you to purchase an external USB hard drive and a type cover and stay at or around your budget. The i3 is not...