Prices will fluctuate much like anything in a supply and demand market. Always expect to pay more for highest quality/purity. It also depends on how close to the source you can get and how many middle men you have to go through. On the low end I see some for just over $100/g and higher end closer to $200/g, though I am sure I have paid much more in the past. Not bad when that makes 50 solid 20mg hits similar to an 8th.
Yes, 4-aco-dmt is the one you are looking for. My personal favorite is 4-ho-met though, it seems to pack the most magic for me.