1) you need a 1 1/8",threadless fork for 700c wheels and suspension corrected. The suspension corrected part is important,because otherwise you'll change the geometry of the bike. Fair number of forks out there;Surly and Salsa are two of the bigger names that make them,but there's also cheaper ones from Dimension. Nashbar makes a CF fork that can be found on sale for around $100 or so. Figure on spending $50-125 on the fork(depending on material/brand),and about another $25-35 to have a shop install it.

2) cheap carbon can be hit-or-miss,I'd at least get a Performance or Nashbar house brand. Make sure you inspect your stem clamp to ensue there are no rough edges,and make absolutely certain you use a torque wrench.