"I would recommend you use your limited budget on one good all around Japanese knife."
I agree, one good knife is better than 2 lesser quality knives. My only point of disagreement with Mark is if I had to buy one knife I would look for either a 210mm gyuto or a 240mm gyuto. That being said, the Kohetsu listed above appears to have a gyuto like profile, just shorter.
One other question to consider is your tolerance for corrosion. Carbon steel will get sharper easier when sharpening, but you will have to keep it clean and dry frequently. Stainless is harder to make really sharp, but it is stain-less.
You might consider one of these: http://www.chefknivestogo.com/fufkm24wa.html
(I have almost bought the 240mm several times, but haven't yet; carbon, totally reactive), http://www.chefknivestogo.com/taku21wa.html
(carbon on the edge, stainless on the remainder)
I would also recommend investing sooner rather than later in a stone. You mentioned that you have other knives you know to be dull. Buy the stone, practice on those, then when your new knife starts to dull your equipped and practiced. Some of the knives above are in the ~$100 range so Mark's recommendation for a combo stone would fit in your budget.
Lastly, I am not sure about handle shape on some of these. You might think about narrowing down you choices in terms of length, profile, and carbon vs stainless, then a recommendation would be easier to narrow down for a lefty.