Does the Ring of Telekinesis allow you to cast the spell as if you are casting it (i.e. your caster level and your Int or Cha modifier) or does it cast Telekinesis as if a level 9 wizard with an Int of 15 (minimum to cast 5th level spells)?
I especially ask in relation to the combat maneuvers because trying to Bull Rush with a CMB of 11 is the same as a 6th level fighter with a strength of 20 so pretty underpowered by the time you can buy an item costing 75,000gp (more than 10th level starting money).
From my understanding the only class of magic item out there that uses your CL / mods instead of the ones of the creator are Staffs. It is explicitly noted in their desc.
As to the cost and balance... You have an AT WILL utility spell. That's nothing to sneeze at. If you don't want it, mail it to me.
Because it's unlimited, forget the CM part of it and jump straight to the "Violent Thrust" part for moving people around. No rolling a CM, just an "Are you under 225 pounds" and "Make a will save or be thrown 90 feet". Failing that, thrown 225 pound of rock at the guys face doing 9D6... Every round til you get bored.
The bulls rush version... probably don't bother. Ranged Grapple / trip is a possible, but if your going to bulls rush, just violent thrust them. The only advantage of using it in CM mode is that they don't get a save (and instead get to try to watch you beat the CMD with +11). For the actual spell when cast, the other advantage is that violent thrust ends the spell, while CM version is X rounds per level... but given the ring gives you unlimited castings, not so much a factor.
The '225 pounds of force" is great too from the Sustained force, even if it is just "I'm carrying 225 pounds of lead shot to hurl at the first smart alec 'I weight more than 225 pounds so there!' creature I find that I can't throw 90 feet/" Also good for opening chests from... (checks AoE on a fireball trap) 45 feet away and pushing the floor of suspected pit traps from similar distances.
The CL and save DC are the minimums of a 5th level spell, as others have said. However, nothing in the general rules about magic items is said about the attack rolls or combat maneuver checks made as part of the spell. My DM allowed me to use my own ability scores for these, since there is no rule that says otherwise. If your DM rules likewise, it makes the ring quite a bit more useful.