You won't find much for that price. This 11.6" Acer Model will run it, but won't be particularly fast because it only has a Celeron CPU and 2GB of RAM (easily upgradeable to 4 or 8GB): http://goo.gl/ECLs4
If you were able to go up to $350 and can compromise on size a little, this 15.6" Asus http://goo.gl/KkU1Z will be faster.
If it really must be $300 or less, maybe you should look into refurbished models. This 14.1" Dell would probably be your best bet: http://goo.gl/EBERx
If you must use MS Office, then your best bet is a netbook considering your $300 limit.
The following 10.1" Acer netbook is the only new netbook selling for under $300 t Newegg. Naturally, there are more places than Newegg to buy a netbook, but they have an excellent filtering system that is sorely lacking at many major e-tailers. Try searching Amazon, they might have a larger selection.