Now you are talking about using 35mm film on a Holga, which normally takes 120 format film. This is a modified Holga am I right? I don't have a Holga, nor am I sure how you would normally mod it to take 35mm film, but my first guess is that the frame size of the modified holga will not be the standard 24mmx36mm size. I could be wrong. Now if you frame size is not the standard 24x36 then you will have to do custom prints if you want just a single image. Outside labs won't be able to print your full frame with their machine. With b/w it will all be easy and cheap if you do yourself. With colour, well, good luck if anyone is willing to do any printing for you.
Are you talking about b/w or colour?