I’d compare several marketplaces before committing, especially if you’re buying placements at any real volume. The same site can be priced very differently depending on the seller’s margins and how much inventory they control.
I’d also look beyond the headline metrics. For example, I’d check whether the site has consistent organic traffic, what countries that traffic comes from, whether the pages actually get indexed, how closely the site matches my niche, and whether the outbound links look natural. A $100 placement on a relevant site with real traffic can be far more useful than a $40 placement on a site with inflated metrics.