I would suggest .NET remoting, but I am not sure that is much easier than a web service.
This overhead is the only reason I have any bat/VBscripts left in my toolbox.
To be honest... I have yet to find a scenario when Powershell wasn’t faster. You will find with Powershell, you always have a lot of options. It is like the old programming adage.
Good, Fast, and Cheap. Pick any two but you can't have all three.
With Powershell... if efficiency is an issue you can spend a little more time with the code and achieve "compiled" code type speed, but it does require that time. Unfortunately most of the samples you see on the web are not performance minded.
In your case… you want to stick with Text Streaming Classes and handle the file and objectizing (my term) yourself.