For a provisional, file it yourself with the advice of an agent - you don't need an attorney just yet, unless you can afford one. Patent law is the one of the most complicated segments of law there is, hence the steep hourly fees.
No matter what process you use, this process is going to take you a long time (unless you expedite the filing using the USPTOs expedited process which will cost you more and reduce your filing time down to 6 months). When you file the actual patent, you will need to be able to prosecute it through the system. The USPTO will argue with you on each point of your patent since they will have 10,000 others nearly identical to it. If you are confident you can prosecute on your own, go for it. But this is where most people end up needing an attorney.
The process can take years and cost hundreds of thousands of dollars. Most people don't bother patenting these days. The question no one has asked on the thread is: do you really need to patent? If your innovation is software-based, don't bother...there is tons of good reading online regarding the need to patent nowadays. Often, entrepreneurs are better off just getting to be the first to market, rather than waiting on a patent to be successfully prosecuted and filed.
In sum: if you have the time, money, and you absolutely need to file, do it. If not, just get your product out there and don't worry too much about IP. Like Nike says, "Just do it."
This will probably raise some ire on the thread but my own attorney is now the Senior Counsel (Patent Atty) for Best Buy, and I've been working with him for over 4 years on patenting a new haptic interface for smart phones and tablets. Doesn't make me an expert on law, but it makes me know something about the hassle and egregious costs of getting IP filed which will immediately be copied a few weeks later, here and overseas. Especially overseas.