DIY post for outdoor sports lighting

Hi all, I'd like to install some reflectors on my property to illuminate a roughly 15x20m area that's used for (dog) sports. The posts that are sold as lamp-posts seem to be crazy expensive. Would a hefty metal section suffice? I can see for example 90x90x5 mm ones in 6m length. I thought I'd bury like 1-1.5 meters underground and set it in concrete and call it a day. Is it a bad idea?