Well, this is a great start, recognizing a problem and asking for help.
You are in a difficult period for a team, years 3 and 4. Teams tend to make a transition during this time as many of the original team members are gone and a new group of students/mentors are trying to take the team up to the next level. I often tell teams if they can make it to year five, they will be around for a long time.
There are no magic bullets, fund raising is hard, recruiting is hard, finding mentors is hard. We have found that outreach is a key element to our growth. We are constantly doing outreach during the year, which leads to networking, which leads to meeting people, and someone in that group of people is going to be the mentor that helps move your team to the next level.
We are in our ninth year and finally starting to see our work over the years turning us into a solid team. We still need more mentors, we still need to improve our fund raising, we are starting to build good robots. Most of this has been driven by the students/parents/mentors we have attracted to our team.
Outreach to FLL teams is an effort that has a big payoff. Many of our strongest team members have come from FLL teams we have met through our outreach efforts (running FLL tournaments and mentoring FLL teams).
The NEMO web site has some great resources you may find helpful.
http://www.firstnemo.org/
Good luck on your journey and keep at it. The pot of gold at the end of that rainbow is worth all the effort you are putting into your team to make it sustainable.