Cox is highly unlikely to get tendered, given his position. It's likely he will just be given a contract around the league minimum, which he would almost certainly accept.
Reed and Harewood are the ones that are a little hard to predict at this point. Harewood has value from a depth standpoint, but he really has done precious little to warrant any type of tender in his first 3 years. He was put on IR and didn't play a regular season snap in his first two seasons, and after bombing badly in a starting role to start the season, was inactive for most of the 2nd half of the year. It's a tricky situation, because giving a tender to a guy who is going to be inactive again in 2013 makes no sense. If he does end up playing a role and playing decently, someone else is going to badly overpay for him, making him basically a one-year rental. He's 50/50 at this point as to whether he even gets a tender.
Same with David Reed, who is darn good as a special teams gunner, but offers no value from scrimmage. A $1.33 tender for a gunner is a totally justifiable if that guy has a role from scrimmage (#5 cornerback or #4 wide receiver). Reed is the #6 or 7 or maybe even #8 wide receiver on the roster right now, so he is not even guaranteed to make the team. Tendering him for $1.33 million takes away some available cap space (about $800k) to use towards another player, so it's hard to see them using that money on him.
I think the wisest course of action is to offer Harewood and Reed a contract that is the veteran minimum for a player with 3 years of NFL service. If they take it, great. If not, then it's time to part ways with them. Keep in mind that the $1.6 million extra towards our cap that they would cost us in 2013 would be the equivalent of the cap # assigned to Corey Graham last year. You can get a decent free agent for a first year cap # of 1.6 million. The odds of Harewood and Reed at this point ever having a lasting value to the Raven organization is minimal, so I think the contractual commitment to them should be minimal as well.
Cox isn't worth $1.33 million, but you don't want to risk losing him either. Why not just offer the guy $3.6 million over the next 4 years with three years of guaranteed money and a small signing bonus? He'd be a fool to turn that down. From the Raven standpoint, it would be a way of securing a reliable player for the next four years. Yes, he'd cost a bit more than the $450k or so you'd pay an undrafted rookie to come and snap for you, but you wouldn't have any worries about that position for the next four years.
They could also do like they did with his predeceasor (Matt Katula) and give him say a 5-year deal with basically minimum salaries and a $600K bonus. That would mean he'd make close ($600K + $630K base = $1.23M) to the RFA tender amount, but would make his 2013 cap number $750K, so there'd still be a decent amount of Cap savings from the $1.3M RFA tender.
Also, understanding that his replacement, even if a rookie (and untested), would be making at least $405K.