I would say this, but it is just an opinion. You mostly want to know if they will be able to spin it and have it retain its softness. I find 100% alpaca a little tricky to work with, myself, for that reason. If I spin it soft enough, it drifts apart. The spinner may ask if you want it carded with some sort of wool (100% alpaca is VERY warm and also has no memory - so that when it is stretched, it will remain that way - no elasticity, is what I am trying to say). Blending with wool would make it less hot and also give it the elasticitiy it needs if you are planning to knit a garment with it.
As for pricing, it is fairly individual, but a good rule of thumb is 10 cents per yard if is is spun as a single or 15 cents per yard if it is a 2-ply yarn. (So roughly $15.00 per 100 yd. 2-ply skein). You most likely would want to go with a 2-ply yarn.
I hope this helps!
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