The cheapest system out there is the Raymarine S1000, but I have mixed feelings on this unit, it has a simple course computer and does not do well to fight a current and stay on course, but this can be easily adjusted by adjusting your heading once in a while. The other issue is some units have issues with holding a course heading under 5mph, and since your using down riggers I'm assuming you will be at or below that speed. Raymarine claims this issue is fixed, and some say it works to about 3mph now, but here is the issue, dealers stock units so there is no way to really know if you have a unit with this update or if it will need to be sent in to be updated by raymarine to accomodate this fix until after you buy it. I've heard of a few guys who say even the new update will not hold under 5mph, but some swear it does, so I guess it is a gamble, nice feature though is the portable remote and the simple hook up and rigging to install it. Cost is about $1000
The next option would be a raymarine S1 or S1G corepack system, they have a more conventional hook up, and depending on how precise you want to be, you can eliminate the gyro feature(the G notation) and also the rudder reference kit(would save about $150). The G is an uprage, I think it was roughly $250 when I priced them out but it could have changed. I bought my S1G for about $1500, I think an S1 was about $1300 at the time, but this was with boat show specials. To me, knowing the system will hold a course at speeds of even 2mph or idle is worth the money, and it seems to run a straighter course at speed as well. The down side is there is more to install.
Raymarine's new X series is great, but will cost about $1000 more, it does eliminate some installation process and cuts down on hardwre in the boat as well as adds more features like trolling patterns, but honestly I would nevr use them personally, but I know some guys do and like them.
Simrad makes the best AP's, but your looking at a price tag of about $2500, but they come with all the bells and whistles for the most part and are very precise and reliable, if you are not worried about price, this is THe best unit to install.
Furuno makes good units too, but from what I've seen for the price you can get the same features for less out of a Raymarine S1g, or get more features for slightly more money out of a Simrad so really it does not make sense to choose this brand unless you were to match all like brand electronics which many perfer to do and is often a good choice to make them work the best together.
I have the S1g from raymarine and like it, it works well and is easy to use. I use it trolling anywhere from 2-9mph for both striped bass in the bay as well as tuna off at the canyons and it has performed great. The s1G also has the option to add for a few bucks more a wireless remote which is a great addition when working the cockpit, keep it around your neck and adjust heading while battling a fish or working the cockpit. If I had the funds I would have opted for a simrad, but to use the system maybe 5-10 times inshore where it goes on only for a few min at a time, or for maybe 5 tuna trips a season the strat $1000-1200 was hard to shallow right now for me. To be honest, not sure hwo I managed without an AP before, will never own a boat without one again.
Thw TR-1 gladiator is nice, but honestly without a display with heading and such it is worthless to me. A good AP needs this, the remote itself is easy to use, but harder to see if it really is doing what you want it to do, to me the unit is over priced. I'd purchase a simrad for a similar price if I had the choice.
Also, most AP do have course computers that update with a sensor, but they utilize your onboard gps when hooked up, and will only work as well as your gps does, a quicker updating gps with a better sensor will allow you to track better and stay on course, the AP is only as powerful as the gps it is set up to. Personally never used a lowrance unit with AP so not sure how they will work but it should not be a problem at all. Sometimes hooking up the nmea cable between non similar brands can be a pain since brands tend to not use the same color wires so splicing them in the right sequence can be tricky at times and other times can be very simple.
I think economically and for your needs the Raymarine S1G would be the most cost effective, and you can add the wireless remote and have control from the cockpit or helm which would suit your fishing needs the best. As good as the Simrad units are, you likely would not need all the features.
