Assuming you're not making a project from scraps and oddments, it is generally true that a large handspun project requires you to buy a large amount of the same fibre. The supply issue can be as much of a deterrent as the project management involved in spinning skein after uniform skein.
Let's take a food analogy. You buy a delicious loaf of organic, crusty bread with lots of seeds on top to make lunch for a few friends. Say you spend five dollars for the loaf and some extra for a jar of almond butter and a jar of blackberry blossom honey to spread on the slices. Lunch goes well. You get ideas about catering lunch for your guild or filling your freezer and pantry with a year's supply for yourself. Now, what was a reasonable price to spend on a small lunch starts to look prohibitive when you calculate the cost for lots of lunches. It's much the same situation with spinning fibre.
A lovely, dyed four ounce braid for $15+ is a manageable cost. That amount of fibre is small-time. Multiply that by six or eight times the amount and you'll want to start looking at undyed roving by the pound or whole raw fleece which costs less by weight. A pound or a fleece costs more at one go and because of this it appears cheaper to buy a braid here and there. Much more colourful, too. Supply shops' packaging makes a quarter pound amount the easy default option to select, just like bakeries sell one loaf in a bag, not a dozen. Therefore, I have turned my mind to consider ways in which these braids can be made to amount to larger quantities.
There's the obvious: buy more of them. I have four of the same multi-coloured dyed braids that I ordered by mail last year on a day I was in a buying mood. I haven't touched them. They intimidate me with sheer numbers. You know how you put off using the good stuff? Four is the highest number of braids of any one colourway I've ever bought and a pound is the most I've ever bought of one type of fibre in one colour. I originally thought I'd make some small items with these braids for other people. Then I thought I'd make one large item for myself, but held off because based on what experienced knitters and spinners told me I doubted the amount would stretch far enough. I can get more; the dye artist is able to replicate the colourway. Maybe I should if it means being able to get on with the project.
New braids would be a different dye-lot but there is not such a difficulty avoiding demarcation with unspun fibre as there is with balls of commercial yarn. You spin a little from one braid and a little from another and thereby blend the whole.
As an alternative to buying more of the same, there is the meatloaf trick where you extend the premium fibre with cheaper ingredients. There are three types of fibre to add, commercial yarn, solid-colour braids, and undyed fibre, and there are a few ways to incorporate them. This post is getting lengthly so I will write about supplementing fibre tomorrow. It's interesting. It gives the opportunity to use more brains than money, and I trust it takes just as much good taste as it does to simply buy more of the exact same pretty fibre.