I bought all my live rock at my local store (LFS). 10 years ago it was about $3 per pound IIRC. So yes, it will cost you a few hundred dollars, but it won’t be the first time this hobby sets your wallet on fire. Some of the “name brand” live rock is highly regarded on here, but I don’t have any experience with it and the generic stuff from my LFS worked just fine for me.
Look around on the build threads here. In general, yes you will want more height in some places in case you ever want to keep SPS with high intensity lighting requirements (place them higher=closer to light), but it also looks like the left side is bare so you could put a structure over there. It doesn’t need to be one continuous wall of rock, though that is certainly an option (kind of how all the old school tanks used to do it). Personally I prefer more depth and varied structures. My tank is basically 2 islands with some overhangs and peninsulas. I had to reboot my tank this year so you can actually still see some of the original rock structure. Here is a photo: