Get an 8x10 from the start if you like those 8x10s from Avedon, etc.
I think the choice comes down to whether you want to enlarge negatives or make contact prints. I prefer the latter and have done various alternative processes with bigger negatives (5x7 mainly). If you start with a 4x5 I think you'll find you will want bigger prints and then you are talking about buying a 4x5 enlarger, big enlarging lens, bigger darkroom, etc.
The initial cost of 8x10 is not that daunting (to me at least). You can find nice 8x10 cameras for $400-$500, possibly with a holder or two. An older 300mm lens in a shutter might run $100 more than newer one for a 4x5. And, I think you will slow down and consider your shots more before you release the shutter with the more expensive, larger film. So, don't think of the film cost difference because you will be shooting differently. There are also some technical differences like shallower depth-of-field with 8x10 lenses. And the bulk and weight are quite different between the two formats. You won't be able to carry as many filmholders comfortably with 8x10, but that also fits with the more contemplative approach of the larger format. It also means you probably won't need to invest in a whole bunch of more expensive holders. Backpacking? 4x5 wins but otherwise I'd go with the larger format. Its apples and oranges really.
And, as others have said, you can probably sell the equipment down the line for about what you paid for it. I think that is probably truer with 8x10 than 4x5.
You can also shoot smaller formats with 5x7 or 4x5 reducing backs on an 8x10.