Pryce moved to Knowsley Road from his hometown club Bradford Bulls during the close-season in search of a fresh challenge and the stand-off role he had long coveted.
Saints coach Daniel Anderson handed the Great Britain international the number six jersey and Pryce has responded in style.
The towering Yorkshireman, one of engage Super League?s brightest talents, helped orchestrate a victory which moved Saints one step closer towards clinching top spot.
The visitors ran in six first-half tries - with Pryce playing a part in five of those scores - and were equally clinical after the break with another six touchdowns.
Mercurial centre Jamie Lyon converted every one of them and, having crossed the line twice himself, ended the match with a personal 32-point haul.
The humiliating reverse for Terry Matterson?s side, coming a week after their 18-0 home defeat to relegation rivals Wakefield Trinity Wildcats, was their heaviest defeat of the season - but a boost to Saints? bitter rivals Wigan Warriors.
Tigers coach Matterson handed teenager Jason Payne his debut at loose forward but it quickly proved a tough baptism of fire for the Academy product.
After Castleford had forced a brief spell of sustained pressure, Saints swiftly assumed total control as Pryce and Sean Long combined to send Jon Wilkin over in the 13th minute.
That set the wheels in motion for a blistering display of attacking rugby which saw the visitors extend their lead after 19 minutes through Willie Talau.
Keiron Cunningham?s meticulous dummy running and offload found Pryce and the former Bradford favourite sent Talau racing clear.
Three minutes later, an audacious dummy from Francis Meli saw him dart through a gap in the home rearguard and offload to Paul Wellens for the first of his two tries.
Castleford prop Danny Sculthorpe had made his presence felt during the opening exchanges but his elder brother, St Helens captain Paul, eclipsed his sibling on 25 minutes when he collected another perfect Pryce offload to race over.
The tries poured even more confidence into Saints and they illustrated as much on the half-hour mark when replacement Maurie Fa?sasvalu took Pryce?s pass to race under the posts.
Remarkably, Pryce engineered yet another score for the visitors before the interval hooter had sounded as his astute offload sent Wellens galloping clear for his brace.
And with Lyon converting all six tries, the contest was effectively over with Saints 36-0 ahead.
Yet there was no chance of the visitors taking their foot off the pedal as Lyon claimed two tries in eight minutes before Kiwi prop Jason Cayless crossed for Saints? ninth try shortly before the hour.
St Helens youngster James Roby broke away to get in on the act after 67 minutes before Long took passes from Ade Gardner and Cayless to go over twice in the space of four minutes.
With Lyon adding his 11th and 12th goals, Saints went 72-0 ahead, but Gray Viane?s last-minute try at least ensured Castleford had the final say, although Craig Huby?s missed conversion epitomised a disappointing afternoon for the hosts.
Castleford Tigers: Platt, Bird, Shenton, Viane, A. Fletcher, McGoldrick, Handforth, Sculthorpe, Henderson, Nutley, Manu, R Fletcher, Payne
Replacements: Kain, Edwards, Huby, Fa?aoso
St Helens: Wellens, Gardner, Lyon, Talau, Meli, Pryce, Long, Cayless, Cunningham, P Anderson, Sculthorpe, Wilkin, Hooper
Replacements: Fa?asavalu, Fozzard, Roby, V Anderson
Castelford Tigers:(0) 4
St Helens: (36) 72.
Tries: Wilkin, Talau, Wellens 2, Sculthorpe, Fa?asavalu, Lyon 2, Cayless, Roby, Long 2.
Goals: Lyon 12.
Referee: K Kirkpatrick (Warrington)