I dualsported my CRF450 using the Baja Designs quick detatch kit. The CRF does not have a charging coil. You will have to have your stator rewound with a charging circuit. This costs about $ 150.00 from Baja Designs. The retail kit price is on the Baja Designs site. You will probably need a mirror. The unbreakable Malcolm Smith dualsport mirrors are about $ 20 bucks. They fold down out of the way when not in use.
The quick detatch kit is great. It only takes about 20 minutes to convert the bike back to mx trim and it only leaves a small wiring loom on the bike. The kit comes with detailed instructions and can be easily installed or removed.
Check with your local department of motor vehicles for what is required. The laws differ from state to state.
How much street driving are you planning on doing? Depending on the laws in your state and how far you plan on riding you can do it pretty cheap. I street legalized my CR250 for about $200 here in MI. The Limitation is that I only have a couple hours of headlight if I run it. For my usage it works great because I only use it during enduros and to ride small road sections between trails. Here's a thread on how I did it http://www.dirtrider.net/forums3/showthread.php?t=143608
If you are in Oregon get the plates and waite for the actual registration to show at the mailbox (2-8 weeks) before spending the rest of the money on the kit. I had plates in hand and on the bike for several weeks when the letter came saying that there was a problem. I was abla to keep the plates and will be legal but the rules are now changed and it sounds as if many coversion bikes are being refused after the fact. Good luck!