At $500, concentration beats coverage: pick the single channel closest to existing demand and fund it properly rather than sprinkling five. For most local services that's either a tight Google Search campaign (a few exact keywords, ruthless negatives) or doubling down on reviews + GBP if your market runs on maps.
Spend the first month's 'budget' on free infrastructure instead of media: tracking installed, GBP completed, review-ask process built, one landing page that converts. $500 into a leaky funnel is a donation.
Set the exit condition up front: 90 days, measured cost per lead versus your break-even, then double down or switch. Small budgets can't afford channels that 'need more time' indefinitely.