TXHC - since you have a Lowrance HDS plotter - if you are thinking about connecting your plotter to the trolling motor to control it, you should consider what you will be up against. Lowrance only works with Motorguide, and Hummingbird only works with MinnKota. Another BIG factor is the generation of your Lowrance unit; for it to interface and work - you must have a Gen2 or later unit.
I have a pontoon, also with Lowrance HDS, and I use my trolling motor all the time to anchor on structure for crappie fishing. I love how my Xi5 works, when it is working properly - which is most of the time (I fish 3-4 days a wk). I've had mine since May last year, and it has been in the shop for warranty repairs twice. The last repair was another defective gps board in the unit.
I would recommend the Motorguide Xi5 mainly because you "might" want to connect them together, AND because the Xi5 holds to structure like nothing else on the market. I use to have a MinnKota, but when I saw the Xi5 in action at least a dozen times, I had to have one. You can easily stay under your budget with the Xi5 - with PinpointGPS, and the Motorguide gateway cable - should you decide to connect them together.
I've talked to Motorguide many times and they assure me that they have worked out the bugs in their hardware, and this is why I feel OK about recommending the Xi5 to you.
So, with that in mind here's what I would suggest:
Xi5 with PinpointGPS - with the built-in sonar transducer
80 lb thrust minimum
shaft length will depend how far above the water your bow sets. There are several websites that will help you choose the correct length.
Get the Motorguide quick release mount so that it is easy to remove it from your boat when you want to.
If you are considering mounting it up front - think about how it will interfere with other water activities to minimize issues. This is the main reason I went with the quick disconnect mount; so that I could get it out of the way when the kids are swimming, etc.
Hope this helps!