The delving party found an alicorn, a unicorn horn, amongst the junk and refuse of a goblin storage room. Bill's player is interested in making a magic item out of it.
After some consideration, I believe Bill may be capable of creating the Alicorn Spear but it is an expensive, involving, and uncertain project. Bill would need to spend 6,000 silver on equipment and rare materials for the rituals and construction, and would have a 45% chance of success. He can improve the odds by acquiring rarer and better quality components: 12,000 silver would give a 70% chance, or 18,000 silver for an 85% chance.
It will also require time. Bill can go into seclusion for about a month and a half, doing nothing else, and spend all the costs at once. Or, he could work on this project in his spare time, paying the costs gradually as funds become available. However, this start-and-stop procedure is much less efficient, requiring about 60 days total devoted to the work.
Additionally, since the horn was in the possession of goblins, there's a good chance it had been taken by force, and may have been tainted by a unicorn's murder, or corrupted by its time in the underworld. Bill would be well advised to seek out a unicorn to purify the horn. If he relies on his own rituals to purify it, there is a small chance (call it 15%) that the result could be a cursed artifact, warped by the powers of chaos.