To shoulder-carry a bulky gun like that, make sure to budget for a full-cut cover garment! On the original question, I am not so sure there are many comfortable shoulder rigs in your price range. I have an Andrews Monarch, for a P229, which I really like, but the only time I wear it is when I am going to be seated in an air-conditioned vehicle for long periods of time. I see them on evilbay periodically, and even those tend to bid higher than your price range. I have an old Weapons Systems nylon rig for 4" sixguns, for which I paid less than $100, but that was quite a long time ago.
I have an Unkle Mike's nylon vertical shoulder holster . It really isn't too bad and it is under $100 (actually I got two of them - one right handed and one left handed - for $5.00 each from a bargain barrel. I combined them to carry two 1911's. Don't ask why.) They are decent holsters. I much prefer my Galco shoulder Holsters, however. I have one for my 1911's and one for my Beretta 92. I rarely carry my Beretta, but Galco makes a very good shoulder holster. It will probably cost $150 but it is worth it.
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