What exactly about being a startup makes this a lot harder? I'd expect a startup would in many cases have a fairly easy time answering requests like this, since it won't have built years worth of legacy systems, half-abandoned projects, weird cross-department data accesses etc that could catch a large company here. You'll likely have fairly centralized storage and a reasonable number of service providers you use for specific purposes. + the typical startup has more or less the same relationship with every customer, so it should be fairly easily repeatable once you've documented it once.

For the few small companies I've worked for, this would have been a bit of work once (document the dataflows), and then a fairly easy set of queries to be repeated each time.