I have realized that "Low Cost" is a relative term...
Can I get a usable asset on the asset store for $30? What if I can only use 25% of it? WHO CARES! GET IT!!! Why?
1) It's probably of a high enough quality because its on the asset store. I don't know about Unity, but UE4 assets are all vetted.
2) My time is worth money.
3) Paying an artist to create the same asset would cost about $2,000 (80 hours * $25/hour)
Even if someone puts a collection of assets up for $100, it's still "low cost" -- It's much cheaper than $2,000.
If the asset is 80% of what I need, that's also 80% of what I don't need to build. The artist can do the remaining 20%. Suppose the asset costed $100, and I pay my artist $25/hour, and the purchased asset is 80% of what's required, and my artist has to put in 2 days to tailor the asset to fit 100% of the requirements. The true cost of the asset was $100 + (16 * $25) = $500. This is still cheaper than hiring the artist to spend 80 hours to reproduce the same work ($2,000).
Edit:
The way to look at the cost of an asset, is this:
Creating an asset from scratch costs $25/hour. For the asset price of $X, is $X + ($25 * TimeToFix) < $25 * EstimatedTimeToProduce? Then its more cost efficient to pay $X. Keep in mind that estimated time varies wildly, and $25 is also a variable which changes by required skill set value.
You only lose if TimeToFix >= EstimatedTimeToProduce.
So, "free" may make $X == 0, but that may also mean TimeToFix < 0. We'll call this "Free_TimeToFix". If you buy an asset, the "Pay_TimeToFix" value may be such that "Free_TimeToFix" > "Pay_TimeToFix", so spending money on an asset may actually be cheaper than getting a free one. And if you think "TimeToFix" == 0 for all assets you get from someone else, you are either delusional or have a very low quality bar.