DAW = Digital Audio Workstation! So tools like GarageBand, Logic X Pro, Abelton, ProTools, etc. basically a central program to edit and splice audio files and midi together
Average costs range spectacularly, it really depends on factors like quality/project goals/etc. You can technically produce ANYTHING for free if you already have the tools and the means. But if you want high quality recording, studio sessions can range from the hundreds to the thousands. Home studios are way cheaper but if you're not really familiar with audio equipment stuff then it can be a little daunting to start building one out
I am a mac user so I use Logic X Pro as my main DAW and I use MuseScore for notation. If you're on mac, GarageBand is free and I think PC users can download Reaper for free but I've never used it? Otherwise, you'd have to pay for other DAW. MuseScore is free and it's never let me down so I haven't bothered to upgrade to Dorico or Sibelius (RIP Finale for those of you who know the tea lol)
I'm not sure what you mean by help? There are plenty of music forums and groups online you can join where you can meet people and ask specific questions!
Same thing with singers, you can search the internet and find folks. Alternatively, you can just go out to small local shows! Meet singers and support their art! It's honestly the best and natural way to find likeminded people to collaborate with