Lots of cheap stuff on E-Bay, especially if you can accept stuff that isn't cutting edge.

As far as "matching", some must, some it doesn't matter. Sometimes new + old stuff matches better.

What I would suggest (and maybe you've done this), is to start with a list of features you want, then the rest should fall into place. It will be hard for anybody here too give advice without answers to those questions too.

• On Road? Off Road? Gravel?
• Brake Type (Calliper, Canti, V-Brakes, Mechanical Disc, Hydraulic Disc)
• Tire Size.
• Frame?
• Bar Type (flat, drops, something else)
• Front & Rear Gearing & Number of speeds. Single/Double/Triple Front? IGH?
• Shifter Type

That will mostly define your bike, and you will be able too quickly fill in the rest.

A 1x11 flat bar groupset wouldn't be my choice, but each person's choices are different.