$500 is quite good amount of money to invest in Bitcoin. You don't need to invest in Bitcoin with huge money in the early of your journey in Bitcoin investment. Just get sufficient knowledge and experience first, then you can increase your funds in Bitcoin investment.
If someone has $500 to invest in Bitcoin, I would suggest they do DCA and buy $50 or $100 a week. Did you notice the recent movement we had earlier? Bitcoin was over $45.5K and then suddenly it touched 41K in an hour. This was the perfect opportunity to buy some sats. If they use centralized exchanges, it's easy to place orders with limits.
You could place buy orders at several price ranges so you don't miss the dip. But, I do not recommend anyone using centralized exchanges even though I use them. Some centralized exchanges implement DCA methods too. Users could set up their preferred settings to buy Bitcoin.