Generally, it depends on how good the professional is. If he’s very good, then I’d hire him and get the job done properly. A Spyder 5 or a xrite i1 Display Pro aren’t sufficient alone. You would have to buy a spectroradiometer, software, test pattern generator and you still wouldn’t reach the accuracy that a professional could give you. Just be sure that he is good and he uses pro level meters and TPG (jeti/CR/Klein/Accupel/Murideo). For a gaming only display, I don’t know if I would even bother to calibrate it, as I don’t even know if software houses do some kind of color grading on a specific BT reference. I’m not a gamer anymore. Anyway, if you want to calibrate it just hire a real pro.
TVs: Pioneer PDP-LX5090H, LG OLED55C8PLA | SintoAmp: Pioneer VSX-921 | BD Player: Panasonic DMP-BDT260EG | External LUT box: Entertainment Experience eeColor | Softwares: Light Illusion Lightspace HTP, Portrait Displays CalMAN Home Enthusiast 2018 R3, HCFR, DisplayCAL | Probes: x-rite i1 Pro 2 - i1 Display Pro OEM B-02, basICColor DISCUS | Test Pattern Generator: DVDO AVLab TPG