a 5-series of that age probably has a residual value in the 250k range if in good condition. but in that condition.. wala na sigurong bibili unless they have the same car and kakarnehin nila parts niyan. which is also your option.

it might not be cost-effective to repair it anymore even if you can find a cheaper source of the cylinder head block. buying on ebay certainly is an option but the shipping cost will kill you. and you have no guarantee that the engine you'll get is not also suffering from loose compression.

figure the engine to cost at le ast $1000 plus drop-shipping to your freight forwarder perhaps $200. it's the US-PH cost which will really get you. The cheapest quote I got was from Johnny Ocean Cargo, $25 per cubic foot but it would take 3 months and someone would have to drop it off at Johnny Ocean Cargo office.

plus that's a 5-series. an E30 would be around the same age but probably easier to maintain.