Gah! I DONT GET IT!

Hey, Fellow Knights! I have been playing this game for some time now but I dont understand this: Why do people sell Brandishes with UVs for so much CE!? There are some like for 5k CE. Someone can buy a Grim Repeater from the supply depot for LESS than that! And I have also heard that when crafting, UVs cannot be transferred to that crafted weapon. So why do people sell only 2* weapons for a big amount of CE?!
Thanks in Advance!

You heard wrong. You can transfer UVs when you craft an item up, however you just don't get the insanely small chance of getting a new UV when you craft the item. The idea is that you buy a tricked out 2 star brandish with loads of UVs then craft it in to what ever you want, transferring the UVs when you craft up.

The other responders have pointed out your misconception about crafting. To learn more, reading the wiki page "Crafting", particularly the section "Upgrading".
To understand why a Brandish with CTR+4 might command a high price, you might read my guide to UVs from Punch. Based on our best data and some basic probability theory, your expected cost to get CTR+4 on a sword from Punch is 2,666,667 crowns. When energy costs 10,000 per 100, that translates to 26,667 energy. That makes 5,000 energy look like a great bargain. And the cost of upgrading a 2-star Brandish to a 5-star Combuster is tiny in comparison.
Now you specifically asked why I would want such a Combuster instead of a Grim Repeater? I already have a Grim Repeater and most other styles of weapon. I'm done collecting weapons for quantity. Now I want quality. I want the best weapons possible. That means CTR+4 (and ASI+4) on my Combuster.

As someone who has blown an 8 figure amount of crowns on rolling, I can tell you UV's are underpriced. If you wish you try and achieve the UV's by crafting or rolling yourself go ahead and try. Though i would highly recommend you go for med UVed items. CTR/ASI med brandishes are very reasonable at 70-80k.
@Encleaven
Yeah, rolling is very risky. I've rolled a million crowns at one time and only got asi or ctr med. But like a few months after I started playing I rolled ASI VH on a flourish in one roll (this really sounds too good to be true lol). Made it a point to show it off to as many people as possible before my ignorant noob self undersold it for 18k E without even using it in LD.
For VH UVs or High, buying is the way to go. Medium is hit or miss (could go either way, but probably better buying). Nobody cares about low

My record for one time roll is 6.8 million. Was trying to roll a 3rd max on my skolver coat (already had a triple max, wanted a second :x). I ended up with Stun High I believe and just sold the thing. Dont remember how much i got for it but even the first two maxes cost a ton, and almost seven mil on stun high as third UV.
EDIT: Did a quick search, apperantly I sold it for only 35k E. Wow. And it was a cap not a coat my bad.

Yeah, rolling is very risky. I've rolled a million crowns at one time and only got asi or ctr med.
Yep. Spending a million to get +2 is not surprising. This is the kind of insight that probability and statistics can give you.
My record for one time roll is 6.8 million. Was trying to roll a 3rd max on my skolver coat...
At 225,000 crowns per roll (the current price), that's about 30 rolls to get something with a 6% chance or so. I haven't calculated the probability of this happening, but I doubt that it's surprising.
Rolling UVs at Punch is expensive. UVs are almost always cheaper on the Auction House, as Lethal-Bunduru said.
I think you have a fact wrong. UVs not transferring over to a crafted weapon is an option, not a requirement. You can craft up an ASI high Brandish up to Combuster, and have it keep the UV. As for the prices, they're so high because of general rarity, and how desirable some variants are.