Basically any/all of the online brokerages will accept you -- will allow you to open a trading/investing account.
You can open a futures or forex account with 2500 to trade. If you plan on day trading you will have to have over 25,000 for an equities account. I am troubled with the way you asked the question. You "need" to start trading? If this is a financial need as in you think you will make a living by trading your 2500 dollar account I think you need to be more realistic. If you "need" to start trading because you have been practicing on sim for a while and you would like to transition to live trading then good on ya!
You didn't state your instrument. Stocks? And assuming you meant brokerage firm: You could 'save up' the extra $500 and consider IB: The following minimums are required to open an account: Individuals age 25 or younger USD 3,000 (or non-USD equivalent) https://www.interactivebrokers.com/en/index.php?f=4969 To understand why IB is a good choice for somebody starting out, compare commissions with other brokers. Robinhood might be worth looking into too. If you wanted to day trade, a possible solution is to trade verrrrrrryyyyy small using a cash account. You'll need to factor in settlement delays.
I would go with TD Ameritrade. No account minimum. No commissions * for 60 days, more info: https://www.tdameritrade.com/specialoffer.page ET Sponsor. * You will need to come up with an extra $500 for the No Commission offer. They require you deposit $3000.