Lol wat ? 2D is way more cheapjer than 3d. You are all trolled by japanese fighting games developers.
Cost of making fallout1 was3mln dollars and back then and 2D 256colour was super high tec.
Pretty much all assets in Fallout were 3D renders, turned in bitmap images/animations.
They wouldn't save one single cent making the game in 3D, they went for 2D just cause computational power at the time wasn't nowhere close to run that stuff in real time 3D.
And if you want achieve some decent standard with your graphics, even today,hand drawn 2D animations are extremely time consuming and pricey to do.
Plus, you should have to renounce at all these advantages in terms of flexibility that real time 3D renders can offer (like showing on the characters what equip they are wearing, being able to rotate it in any direction without any effort, etc).
Last but not least, if you go for 3D assets ported in 2D today, you are going to have the worst side of both worlds. No flexibility and not cool, quirky hand-made look. It really doesn't save you a cent and with the graphical prowess of today's systems is completely pointless effort.