Before you jump right in and buy a nanny goat please make sure you know what goatkeeping is all about.
What are you going to do with the goat kids if you use the milk for lambs? Kids need about 2 ltrs per day (as do lambs) and you would therefore need a nanny that would give well in excess of a gallon a day to have any milk left over for lambs, or you would need a really good-runner through (as goat milked in her second yera of lactation without a kidding in that year). These goats are not cheap, need good feed all year round (to maintain the lactation), a shed, regular foot trimming, vaccination etc etc.
So I would think unless you reallly want to become a goatkeeper, and then use any spare milk for lambs it will be cheaper (on an annual costing) to just buy replacer... If it were cost effective to rear lambs on goatsmilk (by having goats on their farm) many more farmers would do it...
Oh, and never let lambs suckle a goats udder, it will be ruined. Bottle feeding, therefore milking out twice a day is an additional job on the farm...