I agree with the above comments. You aren't likely to be able to get a machine that will do a great job when sticking to a 13" size. Due to price I would suggest looking into a 3rd gen i5 processor (4th gen if the price is there, at LEAST 6 gigs of ram, and plenty of hard drive space. AMD also makes FX series processors, which are no joke, but I personally like Intel more for my application, and they are more available. I would suggest staying away from HP and Dell. HP sucks (I have had one literally melt on me when it was 2 days old), Dell sucks until you get to their high end computers. Sony Vaio makes a good computer, if you get their higher end stuff ($900+), Asus and Acer (sister company) are both very good computers. I personally run a CyberpowerPC and it is amazing, but expensive. Lenovo is alright, Gateway is a bit slower but bulletproof. A tablet style computer will be useless for editing. A MAC is a good choice, but I don't like paying an extra $1000 for the same computer on the tech side. They work and they work well, but what they don't do well they fail at life with.
I would actually suggest going to a desktop for the price. You can get a good setup, and if you do a little bit of research you can actually add components as your budget grows. I actually spent over $1700 on my laptop that a $1000 desktop can do, but for work I needed it to be portable, so my wallet had to suffer. Another thought is to set up a desktop computer as a server and access it remotely with your laptop. It will work as fast as a desktop, but on a portable laptop. And when you need to upgrade storage, ram, processor, etc., you can just buy the parts for the desktop as opposed to buying a new laptop every two to three years. I was actually looking into this, but I personally opted not to simply because in the future I will be building an even more powerful desktop for work (I work with Maxon Cinema 4D, Adobe Photoshop CS6, and Sony Vegas Pro 12 simultaneously. I need computers that can run like a tank).
