This is the rule and not the exception. It seems software always takes much longer and costs much more than you think it will. The smaller the task, the better it can be estimated, and the less likely you are to veer off into crazyland.
The best solution I know would be to hire a team and use agile methodology to focus on the most important things first, breaking them down into small tasks. The team might be people you hire, or it could be people from an agency, but the project needs a strong, hands-on leader who is committed to the goal. I have never known a toss-a-big-solution-over-the-wall approach to work really well. Those projects can vary from annoying to completely dysfunctional.
The best solution I know would be to hire a team and use agile methodology to focus on the most important things first, breaking them down into small tasks. The team might be people you hire, or it could be people from an agency, but the project needs a strong, hands-on leader who is committed to the goal. I have never known a toss-a-big-solution-over-the-wall approach to work really well. Those projects can vary from annoying to completely dysfunctional.