You can get into a a downrigger for a couple hundred if you go with one that bolts on, under a hundred for one that clamps down temporarily. Either way, getting down deep is a primary need at times and 150 feet should maybe be a threshold for max. depth.
If you are going to do this sort of fishing more than once a year, get a couple decent trolling/downrigger rods set-ups from Cabelas. Your downrigger will have a depth counter so the reels don’t need to have one.
I fill my reels with 12 or 17 pound vanish.
Use a 10/12 pound ball and get quality releases, one for the ball and one stacker. I like the fish shaped weight. I think you see less drag with them.
For tackle stop in Duluth down on London Road and go to Marine General on your way up to Two Harbors. These guys are pros and will get the best deal to you price-wise off the un-packaged tackle wall. Its all name-brand, just not packaged to save you $$$$. The terminal tackle like swivels [BALL BEARING] can be gotten here too. The guys here can tell you what the best colors are at the current time, and yes the preference to color will change. Any lure with gold/orange stripe is going to get you lake trout.
Marine carries the lake maps too. Get one. Even though the lake is huge, points of reference save lots of time snooping on wide open water. If you have one, use your gps….it will make your trolling speed easy to monitor [lakers under 2 mph, salmon up to 3.0 mph are my best speeds].
Getting set up cost a few bucks, but the rewards are huge. The biggest investment is the time put into learning. You can streamline that cost by taking someone out in your boat that has experience with this sort of fishing and who can show you first hand what to do and use and how the rigging looks when set up properly.