First, I would avoid making comparisons between antiquity and the Middle Ages. Economic systems, recruitment, and especially sociopolitical structures really make it apples and oranges and fruitless to think in those terms.

That said, Macedon was loaded, and Philip expanded the wealth of the Kingdom of Macedon.

Early on, the forests of Macedonia were crucial for providing the long pieces of timber needed to build the triremes of Classical Greece. From Paul Millet's chapter on the political economy of Macedonia in the Blackwell companion to MAcedonia:

Theophrastus in his Enquiry into Plants comments on the limited areas producing timber for naval construction: within Europe, only Macedonia, parts of Thrace, and Italy. The scale of demand from Athens seems prodigious, with the construction between 480 and 410 of some 1,500 triremes, requiring up to 300,000 oars. In this confrontation of a scarce, natural resource by insistent, external demand, ancient Macedonia might resemble the modern Middle East, with its oil reserves so despertely sought after by the industrial West. The analogy might be pressed further in light of the ongoing involvement of Athenians and others with their repeated colonial, diplomatic and military interventions in Macedonia and its environs. There were also silver mines and other mineral wealth.

But Philip understood money was needed to field his "professional" army. Part of his strategy early on was to secure the lucrative gold mines in the area round him. He began with the acquisition of the mines at Creineds, which according to Nicholas Victor Sekunda's chapter in the same volmue states that this mine gave Philip "the financial resources to keep his forces permanently under arms (451). He also took the mines at Damastium and at Stratonici in easter Chalcidice.

Just check out the collections of the Archaeological Museum of Thessaloniki online. They have a whole section on Macedonian gold: https://www.amth.gr/en/exhibitions/permanent-exhibitions/gold-macedon.