Combined items typically cost (Highest Cost)+2*(Lower Cost)
So combining an item that costs 2000 gp and an item that costs 3000 gp costs 3000+2*2000 or 7000 gp.
One thing to consider also is that he starts with 6,000 xp not 0 xp as he starts as a 4th level character and he should start with equivalent equipment to a 4th level character.