With the momentum of the Dunlap extension, I'm thinking it won't be too much longer before Atkins gets his. With that in mind:
Looking ahead to 2014, the Bengals will have 44 players under contract plus RFA rights to Andrew Hawkins and Vincent Rey ($1.389M ROFR or $2.124M 2nd tender amounts). Boling will qualify for a salary escalator equal to the ROFR tender. Dalton most likely also has an escalator but at the moment I'm unsure of the amount. Peko's salary could also potentially rise slightly due to escalators although I doubt it's significant (~$200k). The team cap will be therefore $113.9M.
Assuming the 2014 cap is a 3% increase over 2013, league cap will be $126.7M but the Bengals should be able to carry over about $10.6M after the Atkins extension (est. 5yr, $48.6M new money, $8.5M '13 cap hit, $10.5M '14 cap hit). This leaves them with $18.2M in cap room. More room is potentially available if some high-cap players are released or have their contracts renegotiated (potential savings includes Peko $3.965M, Wharton $2.875M, Geathers $2.5M).
Michael Johnson will be the most significant free agent in 2014 but a few key depth guys will also be UFA's (Collins, Miles, Mays). However with a solid roster already intact and another 10 added via the draft, the team won't have a lot of holes to fill. The team will likely be an attractive destination for veteran free agents looking to make the playoffs on a reasonable contract. However the main focus will be on extending Dalton and Green.
Green's contract can automatically be extended through 2015 due to a provision in the CBA that allows the team to set his salary equivalent to the transition tag. For 2013 that amounted to $8.867M and with the new tag calculations that really shouldn't climb more than 10-15% since it's tied to the league cap increase rate (I'm oversimplifying but regardless it's less than the franchise tag and there's no risk of another team swooping in with a better offer). This could also be used as leverage to work out a long-term deal either next year or in the offseason prior to 2015.
Dalton's contract is more difficult to judge. He has shown himself to be a reasonably good QB but essentially average. The problem though is that even average QBs are essentially overpaid. We'll simply have to see how he performs this season with an even stronger supporting cast and another year of continuity (coordinator, O-line, etc). Honestly I hope he performs lights-out and gets a fat contract; that would mean the team is that much better as well.