Too often I see engineers bias heavily toward inexpensive, free/cheap, or home-built solutions simply because they personally don't think things should cost money, when the understated anchoring costs of building and maintaining, plus the opportunity cost of valuable people time, might shift the toward other alternatives if a wider business context is taken into consideration.

If we're talking about hosted solutions, I agree it's mostly silly to refuse to pay... unless we're talking about open source projects, where many CI vendors do have a free tier...

Anyway, I also see an opposite bias toward costly hosted proprietary solutions and a refusal to even think about how one could accomplish one's goal with, say, a couple of shell scripts and cron jobs—or a self-hosted open source system.

That bias can be very sensible, but it can also be a hindrance, especially when it turns out that the proprietary solutions aren't quite what you want anyway, but since you're opposed to writing your own scripts, or running a more flexible system on your own servers, you settle for a suboptimal setup...

This bias I'm talking about is also a way of undervaluing something. It's saying "I'll pay $99/month for some hosted thing, but I'll never spend a week of engineer effort on really getting it right."