Lets start by stating, Pentosin CH11S is pretty much one of the best hydraulic fluids you can get. If your system calls for it then don't waste too much time trying to find a substitute as it will most likely not be much cheaper.
We have had some customers who changed out their fluid with one that primes faster etc. but their vehicles exhibited various problems during low ambient temperatures and worked fine once warmed.
Here is the main reason, "Temperature range" pentosin ch11s fluid claims full performance from -40 to +130. that is a bold statement and is mostly to cater for automotive usage. Depending on where you are located, your ambient temperature for life of vehicle can be much different than another driver.
Most other fluids have a much smaller temperature range, similar to how you choose engine oil or octane level of pump gas you use every season. if you are constantly aware of your ambient/driving temps and drive your car based on this. you could use some of the other fluid's by choosing best range for your vehicle.
There is one aviation hydro fluid AEROSHELL FLUID 61 that provides an even greater range going from -40 to +204C and performance vs pentosin, but you have to buy a 55gallon barrel of it.
As we started off, CH11s is a really good product that is widely available online and on many store shelf's across the country. Don't waste your time looking for a cheaper replacement, it doesn't exist.