Your pool cue is from the 1996 Brunswick Magnum Series which was manufactured by Joss USA. Yours is the Brunswick Magnum MG-3 model (aka Brunswick MAG-3).
Here is the 1996 Brunswick cues brochure showing the Magnum cues series. Yours is the third cue from the left.
They had a MSRP of $205 but sold online at most places for $165.
A blue book value for this cue wouldn't be useful at this point as the book is so far out of date. Looking at recent eBay sales is a much better method of pricing a cue. I couldn't find any sales for this exact model, but found two for other Brunswick Magnum series cues. Both sold for values in the low $400 range. Yours, if in near-perfect shape might fetch a similar price, perhaps between $275 and $350 since it's a lower model than the two I found.
The first is a Brunswick MAG-4 from the same Magnum Series by Joss (same catalog, same year, just the next higher model up from yours). This one had an original MSRP of $340 but could be bought at online retailers for $240. It sold for $405 in April 2018.
Joss pool cue made for Brunswick Magnum MAG-4 Model from the 90s
Sold for: $405 (35 bids)
Beautiful Brunswick MAG -4 cue made by Joss USA. I bought this from a billiard store that went out of business 12 years ago (NOS). The cue as been used a handful of times and stored at all times in a case. As seen in the pics the cue is in outstanding condition from the tip to the bumper. I give it a 9 our of 10, with 10 being perfect. The butt weighs 15oz and the shaft 3 5/8. The shaft has an ever slight lift (more a taper lift to me) and is only very very slight. Somebody’s going to get a gorgeous cue.
The second is from the Brunswick Diamond Series by Joss (same catalog, same years, just slightly higher-end models). This one had an original MSRP of $260 but could be bought at online retailers for $195. It sold for $404 in April 2018.
Joss Brunswick Diamond DI-5 Cue
Sold for: $404 (36 bids)
This is a beautiful Joss Brunswick pool cue stick with hard case. The cue is 19oz and is 58" long.