It depend on what coin do you want to buy and how many coin will you buy? The best way to buy some coins with the cheapest price is looking for someone close place that you live and that coin of them. But I advise you should choose big exchange sites like Binance, Bitfinex or Bittrex... you just need to buy Bitcoin and then deposit to those sites after buying the coin you want. You should use Binance because fee trading is cheapest 0.1% even 0.05% if you use BNB token to pay for fee.