It is very hard to find an open source free solution to build a public mining pool. Is there any pre-made, out-of-the-box solutions one can buy?
You can try p2pool which is open source.
I would disagree that it is hard to find open source solutions, there are three pieces of software that need to be combined to create a mining pool.
- bitcoind (or litecoind etc)
- Pool software (pushpool or stratum)
- Web front end (SimpleCoin, mmcFE, MPOS)
I am unaware of any commercial out-of-the-box solutions at this time.