Sometimes there is a cat and mouse game, where candidate does not share their current salary, to avoid a "$X + Y%" situation when the job duties and/or experience would warrant more at the market rate, and the company wants to avoid getting nailed down to a specific number in case they can land someone at less than what they're probably really worth, or in the hopes that they will love the opportunity enough to come on board for slightly less than they might, at the beginning, before knowing anything about the company or opportunity.
In this case, you actually seem to have communicated your expectations, and they still tried to offer you less. It seems like you have had the unfortunate experience of a company that doesn't understand the value of good employees (very short-sighted to quibble over X dollars when a good employee will produce many times more than that disputed amount in superior productivity). Or you are encountering a start-up on such a shoe-string budget that they're not going to be able to compete in the long run.
Either way, it's probably good that you won't be joining them. Job hunting, in general, can be a frustrating, irritating, ego-deflating experience, unless you happen to only really engage on those perfect fit situations. There are a lot of companies and HR departments that really don't know how to do this right, especially with IT professionals, just as there are many candidates who don't know how to be equally good partners from their end of the equation.
The only thing I can think of is if you tell them your expected range, and ask them, specifically, if this falls into their expected range (if that's not disclosed, up front). That does run the risk of alienating anyone who might have these weird ideas that good, obedient production-unit-producers should only be concerned about how awesome it will be to work for their company.
I had an interview once where, because I wasn't looking to leave my company, and I wasn't looking to move to another state, I was up front with the recruiter that it would have to be very attractive, opportunity-wise, and it would have to be a major improvement, financially.
I got to the second interview, and no one had told me anything about the specifics of compensation. Maybe they thought it would take care of itself, but when it came my time to ask questions, I did ask financial questions, which the manager dodged, and then he came back to the recruiter with negative feedback that it seemed like "I was preoccupied with money." I told the recruiter that he set me up to fail by leaving me in an information void about something I was very specific about as a "need," not "want," and told him to lose my resume, if he wasn't going to anyway.