bi-pod - looks cool and is convenient, but not necessary. You could use a backpack, a few blocks of wood stacked, etc. IMO, Harris is the only option if you choose to buy one, as that's what I use. I bought mine used for about half price and it works fantastic.
log book - $.99 Notebook from Wally's World. Don't overthink this one. A ruler and pen will help you make it as fancy as you want.
range finder - Definitely helpful, but expensive! The cheap ones don't work reliably at the ranges you've mentioned you want to shoot at. I'm content guessing a range, taking a shot and adjusting based on point of impact. Once I've walked it on target, that's when I start counting hits and misses. Range estimation is a good skill to have incase your range finder breaks or the batteries die. Also, you can get awfully close measurements on distance using a site like this
, although it doesn't account for elevation changes, only "as the bird flies".
spotting scope - A spotting friend is much cheaper, and more fun to have around. I have a spotting scope that came with my scope and it's about useless. As with anything dealing with optics, you get what you pay for. Buy nice equipment and cry once instead of buying cheap and crying each time you use it. A quality scope at 10x will give you a more useful picture than a crappy spotting scope at 24x all day long. If you need a spotting scope depends on a few things. Are you hitting metal (you'll hear the ping) or paper? If you are shooting for good groups and not just hits, the spotting scope will be the only way to see what you shot without walking out to the target.
Yep... long range shooting isn't cheap! Gotta pay to play. Everything listed above IMO is a lower priority than a good scope. Put every penny you can towards a good scope and then start accessorizing with birthday or Christmas presents. With your budget, I agree the Burris FFII 3-9x is about as good as it gets. I shoot their 4.5-14x on my .30-06 and it's a quality scope. The Ballistic Plex reticle is a good option compared to a standard crosshair. Mildot or something like Vortex's EBR-1 reticles will be your best bet once you learn how to use them and know the ballistics of your specific rifle/cartridge combo.