It's seems contradictory to say that you are targeting the "enterprise" and yet they "can't afford it". Either you're going for thrifty startups, who are not enterprises, or enterprises for whom a few thousand dollars a year is chump change.
I have seen at least one online accounting app that is "free for startups" - that is, you don't have to pay until you have a minimum amount of revenue. I think it was ClearBooks.
I think the best advice so far is in fact to learn other tools in your spare time and work on some open source and personal projects so you have something to show. Start a blog to describe your experiences. Send a potential employer to look at your blog and projects and they will see someone who (hopefully) communicates clearly and codes well and thus will want to hire you.
Any comment on why you want double-entry book-keeping as opposed to simply tracking income & expenses?
Any other requirements you might have?