My feeling is that...

Once you complete the forms with the help of either lawyers or other experienced guys (e.g. your fiends who have already gone through this process), you may think it is a very easy task.

However, if you want to DIY all by yourself, sometimes you may run into some unexpected mistakes, which might cause enormous anxiety/time (let along $).

Also, the lawyers or other experienced guys may provide you with some tricks and better ways to prepare the documents (petition letter, reference letters, pachaging, ...).

So think twice. If you are absolutely poor, you may want to DIY or seek help from any public discussion forums (wenxuecity, mitbbs, immigration.com,...) or experienced friends if you are lucky to have some. Otherwise, spending some money can buy you a peace mind and could save future time/money, provided you hire a responsible lawyer.

This is my two cents. Good luck.