I would have it all done, I doubt any tester would reduce the price to do a portion of it. From when my DS completed this test, both times...it didn't take a really long time (compared to the IQ testing ) I would figure that the fee would incorporate a certain standard of time, and time to score/report etc.

The WJIII was the cheaper test when we had DS professionally tested last summer.

Does your school district by chance use the WJIII? A lot do for academic assessment, so you could talk to the special education department at your district and see if you could have them test possibly.