??? How Much Would You Spend ???

Only thing I have learned in 50 years is never spend more than 75% of the current speaker price on any single component ahead of them. The one exception would be for vinyl-based systems where the whole phono chain is considered a single component. So considered, you might pay more for the phono chain than the current MRSP of your speakers.

Tough to find a consensus because we have different budgets and spending priorities - those with larger budgets would usually spend more than those on a more restricted budgets. Rough guess those on a tight budget 3-7k for electronics (pre+amp) and those with loose wallets 10-15k+. Above this amount speaker upgrade becomes an attractive budget alternative.

Amplifier is the most important component after the speakers. At least 50% of the cost of the speakers should be invested in an amplifier and you have to not only look at cost - matching amp to speakers is critical. Rarely any other component will make as much difference as a carefully matched high quality amp.

Systems are called systems for a reason so they should be built holistically - a chain is only as good as it’s weakest link etc.

Or you could go for a pair of Dutch & Dutch 8c and call it done.