The best CPU below $100

[Dirk Broer]

If the last WCG challenge showed anything then it was that we need more cores/threads in the team.
There are two ways of achieving that.

1. Blindy buying ever more CPUs, till the power company cuts you off due to unpaid bills.
2. Buying CPUs that need just as much -or less- juice, but have more cores/threads.

The latter approach is of course the only sensible one. What can you do with your older mobos, per platform?

• AM2: Your socket supports at most dual-core Athlon 64 X2 CPUs. If you still are running with a single core, try to replace it with a dual core of the same -or less- tdp.
  You must ask yourself if it is economically sustainable to run such an old board/CPU combination.
  
• AM2+: Your socket supports at most quad-core Phenom X4 CPUs. If you still are running with a single-, dual- or triple core, try to replace it with a quad core of the same -or less- tdp.
  Quad-core Phenom X4 CPUs are only offered 2nd hand, but for an AM2+ system they're a decent upgrade.
  
• AM3: Your socket supports at most hexa-core Phenom II X6 CPUs. If you still are running with a single-, dual-, triple- or quad core, try to replace it with a hexa core of the same -or less- tdp.
  Hexa-core Phenom II X6 CPUs are only offered 2nd hand, but for an AM3 system they're a decent upgrade.
  
• AM3+: Your socket supports at most octo-core FX CPUs. If you still are running with a single-, dual-, triple-, quad- or hexa core core, try to replace it with a octo core of the same -or less- tdp.
  THey are dumping their last FX-es, so be quick
  
• FM1: Your socket supports at most quad-core A8-3870K CPUs. If you still are running with a dual- or triple core, try to replace it with a quad core Athlon or A8 of the same -or less- tdp.
  An A8 has as advantage that it has a IGP running along too and it can be combined with cards up to HD7500.
  
• FM2: Your socket supports at most quad-core A10-6800K CPUs. If you still are running with a dual core, try to replace it with a quad core Athlon or A10 of the same -or less- tdp.
  An A10 has as advantage that it has a IGP running along too and it can be combined with cards up to HD7500.
  
• AM1: Your socket supports at most quad-core Athlon CPUs. If you still are running with a dual core Sempron, try to replace it with a quad core Athlon of the same -or less- tdp.
  The CPU to go for here is the Athlon 5370. When you are using an AMD onboard system with a single- or dual core CPU I can advice you to try and buy a 2nd hand AM1 system with an Athlon 5350 or 5370 as replacement.
  
• FM2+: Your socket supports at most quad-core A10-8750 CPUs. If you still are running with a dual core, try to replace it with a quad core Athlon or A10 of the same -or less- tdp.
  An A10 has as advantage that it has a IGP running along too and it can be combined with cards up to HD7500.

When I checked our local prices for new CPUs today, I saw that an AMD FX-8350 goes for just 73 Euro's. The 125Watt tdp is a bit of a worry though, running 24/7/365
If local prices around your residence at at the same level upgrading won't have to cost you an arm and a leg.

But keep in mind that a decent AM4 board can be bought for as little as $60, and that an up-to-date Ryzen 5 will give you 8 threads too...and a Ryzen 7 even 16!