Hi Therese,
This sounds like a great project. However, in order to ballpark a figure, any agency or freelancer you contact is likely going to want a bit more detail in the specs. It might be a good idea to get everyone involved and hash out what you absolutely must have in terms of features, what would be nice to have, and what you do not want. That will help people respond appropriately to your RFP.
If I may offer another opinion, it may be a bigger upfront cost, but have longer returns, if you consider doing a responsive web site rather than a standalone app. If you go with a responsive site, it's device agnostic, so it doesn't matter if you're accessing on iOS or Android or Tablet or Kindle or whatever. This is not to discourage you from the app, but it might be less hassle in the long run.
Regarding costs. I'm pretty involved in the web community here in Pittsburgh, and generally, the rates for website development here- where the cost of living is pretty darn cheap- is in the neighborhood of $150-185 an hour. Freelancers may charge a little less. One model is "Our budget is xx dollars, do as much work at your rate as xx dollars gets us". You may be able to find someone to do the work for a flat rate (the project is xx dollars, regardless) but fewer agencies do this model because it might be hard for them to make money from the deal. I passed your question by a developer friend, and his response was "Without more information on the specs, it's hard to give an estimate, but it might be at least $10,000, who knows, maybe even $50,000 depending on what features and how much they want or need." Don't take that as gospel- but be prepared for RFPs that come back in that range.
If you want to save money, it might be worth considering an agency outside of San Fran or the west coast. Agency rates there tend to be, like most things, a bit higher than in other areas of the country. This has the attendant issues of communication, but I'd imagine they'd set you up with a Basecamp or Slack account to keep track, and have regular check in Skype meetings and perhaps an in person kick-off meeting.
The last thing to consider is support once the thing is launched. Does this organization have a developer on site or on retainer already? What are his/her skills? Whatever you decide to do, it is important that it matches the skills of the person you have in house, or you have budget and plan for an outside agency to take care of the housekeeping of the site/app on a day to day basis.
Sorry this is so long- hope it helps.
Cheers,
Tracey
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Tracey Berg-Fulton
Collections Database Associate
Carnegie Museum of Art
Pittsburgh PA
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