Most people probably do not understand the amount of hours time and effort that goes into making these mods and i may add... they are free!
Really if you enjoy a mod and spend time playing it you really should give the developer something for it after all you are enjoying all of their countless hours for absolutely nothing, would you spend hundreds of hours working for someone else's enjoyment you do not even know?
Or even better... perhaps you have expertise or knowledge you can lend a helping hand... after all these people who have been building mods have probably spent months and months or even years working on mods and I know from my experience that you just want them to be finished and fully working.
Making a creation from which you have great interest is a very special feeling of accomplishment... But taking on too much work is highly stressful I cannot recommend it, if you have an interest you should really try and join an existing team or get a big collaboration going as being stuck into a job pretty much on your own is a daunting task.