First you have to lay it all out figure out what youll need and find a company that does the training or check with your state academy to see when classes will be held and also how much.
Keeping it to a minimum is tough. Equipment especially. With training alot of state academy classes (atleast in Massachusetts) are free of charge so that helps. And if you get people on your department certified in the training then training costs will definately stay down.
When it comes to equipment you can always try for federal and state grants.
You also need to look at the # of calls in the past where you've needed a Rope rescue team. Then look around and see if another dept. That you mutual aid with has a rope rescue team.
One more thing, cost. Not only intial cost of training & equipment but up keep,training etc. Rescue rope must should be replaced about every 5yrs regardless if it's been used or not.