There are zoom eyepieces available too, like the Vixen Click Stop 8-24mm that gives you a large range in a single eyepiece with quite good quality.
Perhaps if you get one of those or similar you can experiment and will get to know what sizes you use most, and can then lash out on some expensive Naglers or similar.
You would be able to sell it down the track without losing too much money on it.
eg.
http://www.optcorp.com/product.aspx?pid=30-718-78-11589