I’ve had massive issues with metatarsalgia over the last 5-10years. The single worst thing for setting it off was stiff winter boots, with or without crampons (although with crampons resulted in excruciating pain like two of my toes were on fire!!), also climbing shoes without a stiff enough sole.
I have dropped metatarsal heads which are largely genetic (or obesity related) by the time I saw a physio the arch of my foot was visibly higher even to the untrained eye. I know you said you can’t afford custom insoles at the moment, but the £230 i spent on the physio/ insoles was the best money I’ve spent in years, and worth forgoing a holiday for. I just left it and left it due to cost and being to busy and reached the point of struggling to walk some days.