Well, right now it's just "two guys with an idea" that we've been working on for a few years now. We could come up with a modest budget, but we'd need to scope the project to know how many work hours would be needed.
As always, it depends on what you need. And that "what you need" should not only contain development time, but also design, quality assurance, management, etc.
Basically, you first of all have to decide what kind of job you need. Do you need a specific add-on, that is fulfilling your already known requirements and you don't need to change the requirements? Then you could look for a "contract to produce a work", like it is defined in German law and which also has equivalents in less civilized countries. There you only pay for the product and it is the responsibility of the development to achieve your goals. But you can't change your goals afterwards, you have to pay if it is according to the contract.
If you have no idea what you want and can't define requirements that are passing the SMART scheme, your only hope is hiring somebody to do a work for you, a usual employee, which you pay for his time and effort and not for his success, because you can't fulfil your contract obligations in a "contract to produce a work" then.
Generally, it is recommendable to do a mixture of both kinds of work. For the more creative work and for establishing concrete requirements, you employ somebody skilled. And for the known requirements with low technological risk, you offer a contract for creating this specific product and select the lowest bidder.
I am already employed, so the only way to hire me directly is to make me do it for free... which is extremely expensive, since you can't buy it. Of course you could ask my employer. But don't expect anything before 2017 right now.