One thing that will help you speed up the process is to get your measurements down in the rooms that need the work. Kitchens and bathrooms are generally your more expensive areas to rehab. Measure the room square footage, cabinet volume, countertop measurements, etc. This will help you to price out the needed materials on your own (at least to get a ballpark idea). For example, if you know that you will need to replace countertops and tile flooring, you will be able to get pricing on the material costs from you local home improvement store(s) - Home Depot, Lowes, etc. for the needed sqare footage… You should be able to ballpark the necessary appliances as well. You can usually get new lower end appliances for kitchens (dishwasher, fridge, stove, etc…) for under $500 apiece. I always go for new lower end brands, than used high-end appliances.
In my area, you can normally count on around a 50/50 cost for materials/labor (i.e. every $1 of materials will cost $1 for labor). I’m sure this can vary from contractor to contractor as well, but at least you’ll be able to estimate your ballpark repair costs. Remember, the little things add up. Grout, drywall mud/tape, trim, bathroom fixtures, etc. are all things that need to be accounted for.
If your contractor cannot come out personally and bid your job quickly enough for your liking, give him a list of measurements for the things you want done, and ask him to give you an estimate. As mentioned by the previous poster, make sure to build in a contingency percentage (I use 20-25% to be extra safe) for unexpected costs.
One other suggestion… I would not put all of your eggs in one basket with one contractor. Let your guy know that you are going to get three bids on the project and that time is of the essence. Don’t worry about hurting his feelings- this is your business and your money at risk. Having more than one contractor in your list of contacts will be nothing but positive for you.
The uncertainty of repair costs will always be present on your first rehab project. Once you have gone through your due diligence on the material costs, you will feel much better about things.
I always use a three-ring binder for each property with clear plastic insert sheets to keep my receipts in to help stay organized. As your rehab work is being completed, create a spreadsheet with all of your material costs in different categories- budgeted and actual. Once you are finished with the rehab, this will be an excellent tool for you to use on your next project.
Good luck- and remember, you will never feel completely comfortable on your first rehab until you sell it for a profit. If it was easy, everyone would do it!