actually wkhtmltopdf/pechkin both won't support pdf/a-3 and have a not so nice output. aspose is actually really cheap, compared to others, unfortunatly their support is trash: https://forum.aspose.com/t/html-to-pdf-pdf-net-fonts-error-o... i.e. pdf/a-3 does not work on mac (didn't tried linux, but I guess it has similar problems)

btw. itext is a really great library, unfortunatly itext has a problematic licensing and I tought they were jocking after they gave me prices.