I'm in the UK so I can only offer some brief advice:
- a cheap bokken over here costs around £12 ($18)
If you want a good bokken:
- be careful not to get a bokken which is heavily laquered. They often coat a bokken with a dark wood effect laquer to disquise cheap wood.
- get one with a nice thick handle, which feels comfotable in your hands (they often vary slightly) - I usually buy the thickest handled ones I can get, and my hands are small.
- make sure there are no knots in the wood. Look down the length of the 'blade' to make sure it is not bent to one side or the other.
- various types of wood, but for solo practise you don't have to worry too much, as long as it feels the right weight. You may want to get a suburi bokken (solo practise ones - a bit heavier), though I find the Japanese ones to be too short.
My advice is to get a relatively cheap one. What they call 'white oak' is a good bet. Go on the heavy side but don't get something that you won't be able to weild well!