Inexpensive spin-columns

[Lawrence P. Casson]

I'm looking for an inexpensive way to purify the products of a
cycle-sequencing reaction from dye-terminators (from ABI sequencing
kit).  As I need to sequence a hundred or so mutants of the same
sequence, I wonder if the purification can be done for much less than
$3.00 per reaction (the cost of spin columns from Princeton Separations
which work quite well for me - I don't know what's in them).

Thanks for any information, protocols, or references.

Larry