Hello, Hexl!
My CPU temp have same 70-80C before upgrading. Temp was discreased really after changing to P8400.Now CPU temp is 38-41C when OS loaded.It not above 70C when i playing games. But you must do not recover breathing holes of your laptop because heated air may damage it.
I agree, Cpu upgrade will be expensive if seller is vendor
You can find it at Ebay stocks.Some shops solding laptop-parts (dissassembled unconditional laptops often or used but working).
I bought my 2 CPUs for 35$ each. (One was bought separately in shop of used laptop-parts and second cpu contain in unconditional dv5 laptop without lcd panel, hdd,ram,ac adapter)
You may try to find sellers of CPU in your region.Trust me, upgrade to P index CPU will discreased core temp very effective.
I think, used cpu is not expensive because it not producing in present time.
This CPU have lower voltage than your CPU so undervoltage is good solution in some situations.
Our motherboard supports 1066 Mhz FSB so DDR3 may be installed but not in this laptops.
Your current Cpu have 2.2 Ghz frequency, 800 Mhz FSB and 2 Mb cache.
Our motherboard supports Intel Core 2 Duo P9700 (2,8 GHz , 1066 Mhz FSB, 6 Mb cache).It's safest upgrade if you want to overclock your laptop.I not found clocks and voltages management so BIOS overclocking is not impossible here.