If you only have $2,500 to invest then I suggest you invest in education for yourself. You can at best hope for 8%-12% annual returns in stocks which is approx $250 per year. Increase your education and you annual income can go up $10k+

I know it's irrelevant to your question but I promise you it will make you richer than investing $2500 in stocks.

in some cases you can probably start with an amount monthly which builds up to a point that something can be purchased

most stock sales have a minimum which can be purchased

Mutual funds. Unless you are a stock broker you should be buying good mutual funds.

yes