So, you are wanting to buy an account with the partyhat already on it? You should be posting in the accounts section rather than here.
Most of trades you see in this section involve the buyer paying real money in addition to the in game trade price. So, for a white phat, you could expect to pay $250-270 plus about 507m in game.
The reason a seller won't just give you the account with the partyhat on it is because after the trade the seller can then sell this 507m gold to others, which at a cheap rate would bring in at least $500 more.
On top of that, you are looking for this on a very low level account, which makes it even more rare.
You are looking for something probably worth over $800 and only paying $350.
Good luck finding someone to do this.