There are garages/surface lots and meters (coin with 2 hour limit). Some garages are very cheap, but then they are not near anything.
I want to say that meters are in effect until ~7pm on Friday (maybe it is a bit earlier). They are in effect on Saturday for sure, I think all day/same as mid-week. I think Sunday is free. The exception to this if you are near the West End, I think those are in effect later in the evening.
There is a garage map online:
http://www.downtowndallas.org/ForRes...ingAround.aspx