I purchased a Topcon RL-H4C rotary laser level a few years back for just under $700, I also needed to purchase a tripod to mount it to and a telescoping rod for the receiver, which was a little less than $100 for the two. There is no GPS capability, but that's not something I knew existed, so I have no suggestions for them or experience with them either. I like to print maps and draw my layouts with color pencils instead of using the computer, but GPS capability may possibly be easier. I've seen kits for the different rotary lasers that includes all you need for around $500 and less, but there's something to be said about making a purchase once for a quality item.
I settled on the model I have because of it's quality, and it's performance. The battery's last a long time, I just looked it up and it says they last 100 hours, it has a 2600' range, and a 5 year warranty. I also purchased some 10000mah nimh batteries with a charger, I haven't kept track of how long the charge lasts with the larger batteries, but in almost three years of using it I've only charged the batteries once, about a month ago, and the same with the receiver batteries....though I don't use it every single day, or even every week, or month. But when I do use it, I have it on all day. I've been quite happy with it. It makes it very easy to get work done. The bunyip in very dense trees would maybe be a little easier with a very long tube, but I haven't needed to use it in such an area so I can't really say.
I don't know why the equipment you were looking at was so expensive, maybe because of the GPS?? But even if you needed to have a rotary level shipped from a different country I can't imagine it costing that much more....though I really don't know. The model I have can be found on a lot of websites, it's fairly popular. I purchased mine from amazon.
Maybe you can rent the gear if you don't need to own it? Though if you have a large piece of ground you may need to make multiple rentals over time which may add up to the same cost as owning it?
I don't have any clever suggestions, I just wanted to give my opinion/experience.