Edit: Oops, hit post a little to early. Sorry for wall of text
I'm in the process of playing a Cleric for a newly started campaign. My DM and group kind of implied that they wanted me to pick up some slack because they are all playing "flavorful" characters. We are at 3rd level now. Our group consists of a Paladin going into Pious Templar, a fighter going into Dwarven Defender and a Rogue going into a homebrew'd version of assassin. Not a single true caster among them. The DM is not a big stickler on one PrC at a time or anything, so long as all of the PrC's have some relevance to my character and I play consistently.
I won't be anywhere near as magic item starved as it sounds like you will, so that obviously changes things. But, with just a Reliquary Holy Symbol (MIC) and a +1 cha bonus you should be able to swing 2 persists out of this build. This isn't the exact build I'm using, you would have to drop 2 levels of Sacred Exorcist and add in 2 levels of Divine Disciple from PGtF, but you don't have access to that book so I changed it a little.
Obviously my situation is a little different, but maybe you'll see something you like.
Cleric 3/Church Inquisitor8/Divine Disciple2/Ordained Champ3/Contemplative1/Sacred Exorcist3
Flaws - Inattentive and Shaky
Progression
1 - Cleric
War (to qualify for OrdChamp and Holy Warrior)
Planning (Extend Spell)
Flaw - Extra Turning
Flaw - Extra Turning
Human - Persistant Spell
1st level - DMM: Persist
2 - Cleric
3 - Cleric - Power Attack
4 - Church Inquisitor - Trade Inquisition Domain for Knowledge Devotion
5 - Church Inquisitor
6 - Church Inquisitor - Strength or Law Devotion
7 - Church Inquisitor
8 - Divine Disciple - Extra Domain, Time
9 - Divine Disciple - Holy Warrior
10 - Ordained Champion - Extra Domain, Spell
11 - Contemplative - Extra Domain, Pride
12 - Ordained Champion - Travel Devotion
13 - Ordained Champion
14 - Church Inquisitor
15 - Church Inquisitor- Quicken Spell
16 - Church Inquisitor
17 - Sacred Exorcist
18 - Sacred Exorcist - Whatever
19 - Sacred Exorcist
20 - Church Inquisitor
This allows levels 3 through 16 to have significant increases in power with little "dead" levels. Divine Power and Lesser Holy Transformation at 7, Righteous Might at 9. The Church Inquisitor levels look funny because I was trying to spread them out so that the progression of Knowledge(Local) isn't so early that it ends up capped low.
You might need more Extra Turnings to get Persist to work without magic items. It's reasonable to take the 6th and 12th level feats as Extra Turning and try to get the devotions through bonus domains (probably dropping quicken and using the last feat slot for a devotion feat). I'm planning on getting 1 Nightstick, Reliquary Holy Symbol and Bead of Divine Power (Dragon305). Those with 2 extra turnings and Eagle's Splendor to boost my 12 cha should net 21 turning attempts.
Sacred Exorcist might not be the greatest cap to this, I just figured there was enough power here already. You should be able to end up with close to +20 to knowledge checks by level 20 with this build, before spells or items.
Third level OrdChamp channeling ability + holy warrior + cleric buffs + power attack + knowledge devotion + magic weapon should make for very good melee damage. Lots of side special abilities between the PrC's.
Oh, one last note. If you are going to take PrC's that don't progress turning, then it is my opinion you should find other things to do with your turn attempts. DMM is the obvious choice, but there are some other decent Divine feats. With an underpowered Turn Undead ability, it's going to fail when you need it most, most of the time.