Please take into account that I live in Europe, thus the price of the heat sinks should be different with respect to what you can find somewhere else. I am currently considering these options:
- Cooler Master Hyper 412S (~34€)
Cooler Master Hyper 212EVO (~39€)
Prolimatech Panther (~44€)
Thermalright True Spirit 120M (~45€)
Scythe Mugen 3 Rev.B (~47€) <-- superseeded by Mugen 4
Scythe Mugen 4 (~48€)
Thermalright True Spirit 140 (~50€) <-- no enough clearance inside casing
Cooler Master Hyper 612S (~50€)
Scythe Ninja 3 Rev.B (~51€)
I wouldn't go too much beyond 50€ (65USD, nowadays), so I have already dropped some other options like the Thermalright HR-02 Macho (~62€) and the Noctua NH-U12P SE2 (~60€). I think top-down solutions wouldn't be the way, for the P183 top and back fans next to the heat sink would ruin the air flow.
EDIT: Cooler Master Hyper 212EVO, 412S, & 612S and Thermalright TRUE Spirit 120 & 140 added, thanks to kuzzia and CA_Steve for the suggestions. Prices are referred to Amazon.it/Ebay.it and take into account shipment costs when required.
EDIT: Scythe Mugen 3 rev.B added, thanks to kuzzia for the suggestion. Price is referred to Amazon.it.
EDIT: Scythe Mugen 4 added. Price is referred to Amazon.it.