I'd say you probably would have to do LA and maybe CR individually.

The +2 to three ability scores is already +1 LA worthy, although in truth it's more of +0.7 LA (+4 to one ability score is probably as good if not better depending upon score), although you can go +2 Con, +4 Cha. Thankfully Charisma is (almost) only used by casters and a full caster hates LA.

Halphax is definitely worth more LA due to the combination of DR 10/adamantine and Imprisonment (although as it can only take one creature out at a time that's made much weaker), probably +3 or +4 (by the books it is a +7 before acid-testing).

Orthos, by the books, is a +5 + whatever displacement is worth (Savage Species doesn't say) and then acid-testing would have to be involved. Personally I'd say blindsight and displacement at least jack this up to +3.

Now to look at lower level ones there's Naberius, who'd normally even without the ability modifiers be a +1 LA how they assign LA. That's definitely not fair when compared to a 1 level dip in binder without LA buy-off. At the same time the +4 Con and +2 Cha is actually rather sweet for the characters most likely to dip into Naberius and with LA buy-off it's simply paying something less than 3000 XP for +4 Con, +2 Cha, and several good abilities.

If you really want to do the simple thing (i.e. have a set and sweeping this level has LA +X) then I'd advice putting a hit die minimum on each vestige (hit dice must equal the minimum binder level to bind it), or else just watch for abuse-able combinations (such as warlock + Naberius). Even then it depends upon if you're using LA buy-off.