I agonized over gear for 18 months prior to my first elk hunt a few weeks ago. I worked with our outfitter (Montana native) on what were absolute "must-haves" vs. nice to haves. I think the key is being completely honest with yourself about your long term intentions/expectations. If this is your first ever elk hunt, there are no guarantees that you will go again, and if you do it may not be a yearly thing. So, you don't need to spend thousands of dollars on gear for your first hunt.
Guys on here will laugh, but on our 8 day hunt in the Bob (which was the hardest hunting I've ever done in my life) we hiked over 30 miles of scree slopes, near vertical mountainsides, dark timber, you name the terrain we hunted it. During that time, I had amazing luck with a pair of
uninsulated 6" Redhead GoreTex trackers that I'd worn the previous pheasant season in Iowa. They were well broken in, and I had cleaned them thoroughly and applied a healthy treatment of leather conditioner/water repellent at the end of last season. Other than this, I didn't do anything special to them and they took everything I threw at them and provided all the support I needed. I used Darn Tough Merino socks the entire trip and this combo paired with Kennetrek Gaiters kept my feet warm and dry throughout. The boots are still right and tight, and I plan to use them again for whitetail and pheasant season in Iowa this fall.
I bring up boots specifically for a several reasons 1) They can be one of the most expensive investments for a first time western hunter ($200-500); 2) they are critically important as they are what connects you to the ground; 3) for some they can make or break a hunt if you have weak ankles, knees, hips, etc...; 4) they directly impact your level of exertion, how worn out you feel after a long day, and ultimately how hard you can hunt over a period of time. With my outfitters blessing (his packing list recommeds Schnees, Kennetreks, or similar) I successfully rolled the dice with a pair of boots that many wouldn't consider for the hunt, but they were perfectly adequate for me. That being said, we used mules to pack out and didn't wear big frame packs for hauling out meat which for some may demand taller and stiffer boots.
I should mention that I'm 6'1 and 225 and in relatively good physical shape for a 46 year old. The money I saved from buying brand new boots paid for my half of the meat processing and one nice dinner during our trip.
*EDIT* The OP also asked about rain gear. This was another item I struggled with, because I had an older soft shell Gore Tex parka and bibs for deer hunting. To make a long story short, after discussing with the outfitter, I left the bibs at home and brought the parka and a mil-tech poncho for our hunt. The poncho was around $60 on Amazon and was phenomenal on a day when it rained and snowed on us all day. Huddled up under a tree with my poncho on top of everything I stayed 100% dry.
