I'm on here out of interest/learning (no knowledge or experience of MIG brazing whatso ever), but it strikes me that if you've found some wire that's extremely cheap it could be a really bad gamble. With many things cheap consumables are cheap for a good reason, they can be rubbish. When learning a new skill the last thing I'd want is to risk starting with something that may not be up to the job. If you know what you're doing you can sometimes cope with substandard stuff, but as a learner it might end up causing you to get poor results, get frustrated and ditch the process as being rubbish when it could actually be faulty wire. Personally I'd be spending extra on something that I knew would be good, and give myself a fighting chance.