What kind of high are you looking for?
I have a few ideas...
singleseedcentre.com ships individual seeds of many different breeders to the us. That will let you try out many more strains for your money. Then if you find something you really like, you can go ahead and order a whole pack if you wanted.
In my experience seed boutique is consistently cheaper than attitude, especially once you figure in shipping.
If you like sativas, check out satori by mandala. Very easy and quick plant to grow, high yields, and an excellent, long lasting high.
Subcool's gear is pretty reasonably priced, and a couple of his strains are @ right at the top of my wish list.
As mared juwan mentioned, cannacopia has an excellent rep, but I have not tried them myself.
KC's strains get very mixed reviews, make sure you research whatever specific strain of his you want to order first.
I am guessing with your 5kw of lights, that this is a commercial grow. I would recommend getting a few individual fem seeds of several different strains, then see which one is most popular where you live.