You live in a city that I am sure must have several martial arts supply stores, I'd check out the yellow pages and call a few for prices, then visit for quality. I'd expect to pay around 40-50 for one you will like and that will last. You can get them much cheaper, but the quality goes down and you would rather buy one that will last than several that won't.
Since you say it is for solo practice only, Ian is right, you could go for the cheap wood (no one will be hitting it), but you never know, you might want to start practicing with others. Besides, I recommend light sanding and oiling, and you hate to invest time and effort in something poorly made to start with.
I would buy from a local place over mail order if possible, unless it is a very well known mail order business (again, since I like taking care of the wood, I like seeing it and choosing it out of the stack at the local store, not getting it in the mail).
If you like what your dojo/club uses, you may want to ask your senior students or sensei where the weapons are bought for club use. I hate to disagree with Ian, but I would choose a handle based not on bigger is better, but on your hand size; it needs to be right for your hands to hold in the correct position.Most folks are about the same size, but if you were significantly outside the two standard deviations, you might need to look for a specially sized bokken.