If you feel comfortable, you can apply by yourself. You may also find some lawyer that charge only $1500 or $2500. One of my friend retained a lawyer who charge him $4000 for NIW case, denied, appeal, denied agin. Then he retained another lawyer with over $10K fee, applied again and got approved. I am not saying that expensive lawyer is better, indeed I saw some crapy lawyer charged a lot, only because they will take good case which will give higher approval ratio. Here are some of my points to have a lawyer:
1. You need a lawyer to do the case, not a secretary;
2. The lawyer should respond to your question ASAP;
3. The lawyer should be confident with his work. For example, the laywer will charge small amount for the kickoff, then charge the larger portion of the fee upon approval.
Ask your friends and get recommendation from them is very important.