"realistic"
None of the top 4 are signing with a bottom club.
Hayne/Dugan if you over-pay them
The Knights already have Gagai and he isn't exactly winning games for us
Matulino yes
Gordon has one season left
Lewis will re-sign or retire
try again.
Gordon is a great choice. Tigers need a few seasoned players to pass on their professionalism, even if only for a year, and a few good young/ mid career options. They could also try Kahu, or Nightingale or Tupou at fullback. Roberts is going great and might get squeezed out if Hayne re-signs with the Titans.
They probably need a centre. SKD, Ferguson, Lafai, Beale, Chambers all solid options.
Tigers could probably get a fullback and a centre from those lists for under the cost of Tedesco.
They need a new half, or maybe stick with Littlejohn. Otherwise, Townsend is a strong option, or Nu Brown as Townsend is keeping him out of firsts. Josh Reynolds would be a great fit, bringing some passion to the games. Widdop would be near marquee without quite the highest price. Roberts could also come over as a half. Mitch Cornish hasn't had a real crack at the top grade and could go well under Cleary.
They really need a hard edged, experienced forward. James Graham would be ideal, but they could also go for Guerra, Heighington for a swan song back at his old haunt, Glenn (if he hasn't re-signed- not sure if all these suggestions are still available), Hoffman, Lewis, Tupou, Blair, Matulino.
Then some more hard workers or potential forwards currently under achieving, like Tagatese, T-Rex, Gubb, Grant, Ofahengau, Taylor, Lillyman, Asofa-Solomona, and Thompson.
They could try for Peats, and make him a leader of the club, or stick with McIlwrick, who is doing well.
They can try Super League. Whitehead and Hodges have made great transitions. There'd be plenty of players, even marquee Super League players, who'd love the chance and the coin on offer in the NRL. They might be able to get a gun forward like Roby, Farrell, Bateman, O'Loughlin, Jones-Buchanen, or McMeeken.
They could try for a handy Aussie who wants to come home, like Kelly, Millington, or Hinchcliffe.
And there are almost certainly some "gamble" options on young players who I've never heard of who could come good, and "out of favour" players like Barba, who could come back and tear it up.
The Tigers need to instil some grit into their team, and there are plenty of decent options.