You have three basic options.
First, you can try to sell the unit and work out a short sale. That is where the unit would sell for less than is owed and the lender would agree to release the note and mortgage in return for the net proceeds of the sale.
Next, and this is what you are referring to in your question, is a deed in lieu of foreclosure. That is a negotiated agreement where you voluntarily deed the property to the lender without the lender having to go through the foreclosure process. As part of the negotiation, the lender would release the not and mortgage. You might also be able to get them to stipulate that the value of the property is the remaining balance of the mortgage. That way, you would not get a 1099 for the amount debt forgiveness.
The last option is to just walk away. It is the riskiest because you have no negotiated terms and the lender could have options regarding deficiency.
It is a good idea to have an attorney represent you. Lenders are notorious for giving unrepresented borrowers the run-around. A general business or debtor/creditor attorney could help you.
As for fees, there is no set rate and it should be negotiated upfront. The fees will be hourly and the cost will depend on the amount of time. Of course, the hourly rate for a large firm will be more than a storefront neighborhood attorney.
If you need assistance finding local counsel try Martindale Hubble (site rules prohibit us from referring specific attorneys) . Many attorneys themselves use this site to locate attorneys outside their jurisdiction or expertise:
It is a huge worldwide database searchable by location and specialty. The attorneys are all peer rated. So, they represent the top of the profession.