Bitcoin mining requires high speed computers and efficient hardwares. Mostly it can cost from few hundred to thousand dollars. Bitcoin by default will make mining a difficult task with time (though miners can earn via transaction fees).
If you have enough time and money to invest in Bitcoins then go for mining otherwise buying Bitcoins is more easy.
Mining is really expensive where you have to buy equipment which you can actually use for buying bitcoin to start an investment. When you get huge profit, you can start to buy little by little the hardware that can be use for mining. Make money works. Buying is more faster to earn profit than mining.