Gut feeling: Hale will retire, allowing around $250,000 or so out of the salary cap. The general feel is that Whitecross and Suckling will envoke their rights as Free Agents (both are probably $150,000-200,000 ish) so that's already a decent amount of Salary Cap space. Though I think he'll go on for another year, if Brian Lake is forced by the Club to retire that's an extra $350,000 dollars in the Salary Cap.
It's not enough to get a real big fish, but $250-$300 could go towards a talented player.
On another note, I really hope that Lake doesn't retire because the only real genuine KPD we have in development is Brand and Heatherly: both of whom are unknowns (really keen on Heatherly's development though, very good overhead mark and reader of the ball like Lake). Another season with Lake while we are arguably still in the Premiership Window (greedy much?) would be fantastic and gives him time to teach the other two his craft.
Personally I'd love to get James Aish to the club as he'd be better than anything we would get with pick 18 in this shallow draft (probably downgraded to pick 20 when Free Agency is taken into account) and is another talented player we could add to our growing young midfield depths.
Apart from that, there's nothing really in our realistic batting range. Players like Bennell will probably get $500,000 at a club like Richmond/Fremantle who wish to add real speed. Seedsman would be alright, but North would probably be able to offer more for him swell as guarantee more game-time.
This Trade Period (probably) isn't going to see us land a big fish like Lake, Burgoyne or look at already established players with further potential e.g. Gibson and Hale but instead take a gamble on players who have potential e.g. Gunston and O'Rourke. Also use one of our draft picks to grab a developing tall forward (that's not a stick).
Of course, I'm speaking out of my arse and have no idea what would happen.