Baseboards are relatively easy to install compared to crown molding. You just need a good miter saw to make 45 degree cuts for inside and outside corners and scarf joints between boards. If you know how to use a coping saw, the job will go a little faster and you can avoid most problems with out-of-square walls for the inside corners.
Tools needed: miter saw, finish nails/hammer (or nail gun - preferred), nail set, coping saw, stud finder, sprit level, sanding sponge, caulk, paint.
Depending on the style you want, you may need cap and shoe molding as well.
Cost by a pro would vary from say $5 to $8 per linear foot to install, caulk, and paint.