Price impact is not a fee and it is not slippage in the classic sense; it is the mechanical consequence of the pricing curve. It is deterministic on an AMM: given the reserves, you can calculate exactly what a given size will cost before sending anything.
Interfaces display it as a percentage and often warn above 3% to 5%. Treat a large number as information about the market, not merely a cost. If a $20,000 order moves the price 15%, the asset has almost no depth, and the exit will be at least as bad as the entry.
Splitting the order does not help on a single pool, because the curve is the curve; only routing across venues does. A dex-aggregator reduces impact by splitting across pools, and for size the honest answer is often that the position is simply too big for the liquidity available.
Related: constant-product-formula, slippage-tolerance, market-depth-crypto, dex-aggregator