Yes. And oh my the role playing options you are going to experience with creative player's like this!
One of the great things about 5e is how little information they decided to put into the Player's Handbook about crafting. This leaves it entirely in your lap as DM, and more importantly, for your player to discuss with you. Your player has stated that what they want is to:
- Create a magical item
- Use the wand as a component
- Use a Kris as a component
- Have the item function as basically a Dagger of the War Mage.
So, we have a couple of handy tools to help you with this. For starters, we'll take the components for this spell as your player detailed them.
DMG pg. 212 - Wand of the War Mage
Wand, uncommon (+1), rare (+2), or very rare (+3)
(requires attunement by spellcaster)
While holding this wand, you gain a bonus to spell attack rolls determined by the wand's rarity. In addition, you ignore half cover when making a spell attack.
PHB. pg 149 - Dagger (Kris)
1d4 piercing, finesse, light, thrown (20/60).
Then we'll take the two items and consider the "weight" of adding the ability to do melee damage would be to this. To do so, we'll take another magical weapon with similar benefits and compare it's capabilities. You'll find that in the DMG, the general rule of thumb for magical items and rarities is: 1 magic effect = uncommon, 2 = rare, 3 = very rare, 4+ = legendary.
DMG pg. 166 - Dragon Slayer
Weapon (any sword), rare
You gain a +1 bonus to attack and damage rolls made with this magic weapon. When you hit a dragon with this weapon, the dragon takes an extra 3d6 damage of the weapon's type.
So, we have a sword capable of dealing damage, that also has a bonus to attack rolls and damage, and also deals additional damage in specific circumstances. The DMG lists this item as rare, and as I said before, you will find that it is often the case that when a magical item has 2 properties it will fall in the rare category.
So, we can go to the DMG pg. 135 and see the Magic Item Rarity table which lists Rare items as targeting 5th level or higher for the character, and costing between 501 to 5,000 GP.
Since a Wand of the War Mage requires an attunement slot (which you are limited to 3 of), I would personally make this a less valuable item, and drop it down into the 501 to 1,000 GP range. In fact, I may even make it uncommon considering the attunement requirement (but that's a personal choice). However, since your player is commissioning somebody else to use it as a material in an attempt to craft a Kris of the War Mage, I would personally double whatever price you set as the price the Wizard is charging for creating the item.
Bottom line, to craft this using the information I provided, I would do the following:
- 2,000 to 2,500 GP cost to the Wizard crafting it
- Wand of the War Mage +1.
- Onyx Gemstone (or other black gem) worth at least 100 GP (you said he wanted it to be a black Kris right? What better way to be magical about this than making a gem part of the material component cost or even a part of the final design as the focal point for the arcane energy?)
- 1d4 weeks to complete it
And that's it. At the end, you've given the player a rare item that has an additional function, but at the cost of an attunement slot. It's also opened the door to creative crafting options at your table.