Does everyone need to buy one of these things to rig the cables or is there something else we can use?

One option would be to tag it as incomplete...plan to make at least the first flight from an airport with an FBO and hire them to to check the cable tension for you (most all FBO's have the tool, it shouldn't be anywhere near an hour of shop time).
 
Meade,

You can spend $800-$1000 for one but there is a cheaper alternative. You are going to need it for your yearly condition inspection. There really is no alternative. An hour of shop time may be 50% of the cost of the gauge.

The BURROUGHS CABLE GAUGE ($180) was the gauge we used at the LSA Repairman's course recently attended. Seemed to work just fine!!

http://www.aircraftspruce.com/menus/to/cableequipment_tensionmeters.html

Or, your EAA chapter may own one that you can borrow. Ask at your next chapter meeting.