Kresimir - I wouldn't prioritize the Deathcleaver. It is a great weapon but you can make a much bigger dent in your build with other items first. The Whetstone combined with the best damage wheel rare is as good as virtually any UR for Barbarians for 2 handed weapons. The ElfStone Shard is a great item and among BiS for Ioun Stones. You can get one for less fully transmuted than transmuting it yourself.
TE's are always first since they help you improve your build over time. You are right that the COA is really expensive right now ($1800+) - until we see a treasure cap, I don't see if dropping in price, though. In my recommendations below, I put TE's right up front. You'll draw tokens you don't need but can sell those via the secondary market to help fund the stuff you really do want.
Others have commented that building a transmute is almost always more expensive than just buying it. This applies to virtually every item. Beyond Auri's Candle (definitely an edge case), I can't think of the last transmute that you couldn't buy the transmuted item for less than building it today.
I find that adding things that make your builds more fun and more viable at NM difficulty is a great way for players to progress. NM usually means more experienced players and more variety in terms of themes, play styles, etc.. PUG runs are fun too but if you have a NM build, that opens most everything to you.
To play at NM, you'd need a to hit of at least +15 and saves around +15 (or work-around like figurines for auto-succeeding on certain saves.) You are close on to-hit, your saves are the crutch.
If you were to spend $400-$450, I'd recommend the following instead of the deathcleaver:
Medallion of Furious Attacks ($300)
Cook's Hat ($110)
Ioun Stone Jasper ($15)
Ioun Stone Silver* (wait for the prices to go down into the $200's. $300+ might be a strange current spike - not sure why it jumped more than $100 in the past year.)
General recommendations for 2022 and earlier tokens:
1. Ioun Stone Silver Nugget - TE's are always BiS
2. Level boosting item - 5th level is critical to strong builds - I recommend Cook's Hat as there are slot expanders coming for Ioun Stones - later get your 5th level with 2 eldritch items (or similar combinations). Cook's is currently about $110.
3. Medallion of Furious Attack or Bog's Medallion (I wouldn't recommend transmuting furious attack but if you get one and later get Bog's, you'll almost certainly sell it for what you paid for it.)
-The Barb class relic/legendary is among the very best. Even the relic with +6 damage, 1 extra rage, and a use of Fury (auto crit) is amazingly impactful. Fury is a
lot of fun to use for Barbarians.
4. Relic Charm bracelets - slot boosters are incredibly helpful for all builds
5. Charm of Glory - Ring is the most powerful slot - pick this up before it gets too expensive (recent OOP)
6. Relic or legendary Havok ring - BiS damage item that will likely keep its resale value if/when you decide to upgrade.
7. Master Ale Drinker's Bead (inexpensive +3 con)
2023:
1. Bead of Bounty (TE)
2. Gauntlets of Divine Guidance (+3 to hit melee)
3. Lenses of Flawsight (+2 to hit melee)
4. Earcuff of Orbits (slot expander)
You have quite a few items that you can keep long term (your 2 TE's, Ring of Dark Health, Belt of the Brave, Charm of the Fire Newt, Enchanter's Whetstone.) There are some other rare or lower level items that you should consider adding that have a big impact on your build:
Ring of Brilliance (+3 dmg w/ 2 handed)
Ioun Stone Jasper Ellipsoid (+2 damage)
Boots of the Bolt (+1 to hit and damage)
I roughed up a build that adds the Ioun Stone you as missing, Cook's Hat, and the relic barb necklace. It could be a good starting point. It meets the pre-req for to-hit for NM (as well as really good damage) but fails badly on saves. It would need something to help with reflex and will saves. Adding a charm of glory for a ring slot then equipping a greater ring of reflexes (really inexpensive item) would get you a great deal closer to a legit NM build.
tdcharactercreator.com/#/character/edit/230637bc-273a-45a5-bd13-ab7a461e7c72
Fred