I am working on an ASP.Net web application that must print dynamically created labels on standard Avery-style label sheets (one particular size, so only one overall layout).
I also struggled with the HTML/CSS approach due to the inconsistent printing behaviour across browsers.
I created a C# library to produce Avery Labels from ASP.NET which I hope you might find useful:
https://github.com/wheelibin/SharpPDFLabel#readme
You can add images and text to the labels, and it's easy to define more labels types.
(I use it for barcode labels, the barcode is generated as an image and then added to the label using this library.)
Cheers