If you are reasonably handy with automotive tools, you can rebuild it yourself. Here is a link to an illustrated posting of rebuilding the steering box:
http://www.chevytalk.org/fusionbb/showtopic.php?tid/225413/Most likely it needs only the steering pitman shaft bearing replaced. I have done it, it is not that hard to do. Chevies of the 40s has the bushing #266316 for $22.50. You likely only need one, the outer one, closest to the engine. They and The Filling Station both have steering box rebuild kits available for $80(FS) or $105(Cot40s). Those kits include the bushing and the upper and lower steering gear shaft bearing sets, and other parts, which you may not need.
This would be a good time to replace the pitman shaft seal, and clean out the box and put in a semi-fluid grease like John Deere Corn Head Oil.