I'm not sure those small portable units are capable of evacuation, I've never used one. There are lots of old R12 automotive recovery machines on e-bay - all of these machines have internal vacuum pumps. The prices of the R12 machines are very low since there is limited demand for R12 A/C services these days.

I purchased a SUN MRC300 on e-bay a couple of years ago for $125. This is a basic R12 recovery/recharge machine but it came with it's own tank and vacuum pump. The only downside to my approach is that it took me awhile to find somebody that had one for sale locally and the machine takes up a measurable amount of garage space for something that might not be used very often.

I think the small recovery units are capable of being used with different refrigerants (if you have a separate recovery tank for each unique refrigerant) but as I recall you have to go through a procedure to remove the refrigerant oils from the machine before you change refrigerants. PAG oils used in R134 and not compatible with mineral oils used in R12 systems and cross-contamination is not a good thing.