JB pumps run anywhere from $350-$900 depending on the model and what not. For purging oil you don't need a 10cfm 2 stage pump capable of 15 microns or anything crazy like that.
@farscaper
The red plug is most definitely for the exhaust port but your correct the exhaust can be throttled if you wish to slow the pump down (Actually mine has 3/8 NPT on the end but it also has a built in ball valve on the exhaust) but I prefer to do that on the intake of the pump where your hoses hook up or via the gas ballast port on the oil reservoir.
Have you checked out the extraction artist thread it outlines a lot of purging techs guys are using pretty thoroughly. However I would say you need to make sure you have a fairly accurate way if getting temps. I also would keep whipping to minimum go for a thin film purge and try flipping it. This helps keep from trapping solvent and moisture in your oil.