350-650 depending upon how hungry the tech is... and whether or not they're having a good day, whether or not traffic was bad, a/c was out in the van, or if we're talking an up and coming shop with all new vans, service equipment etc, I've seen as much as:
'ahem, well your spa is too old and you need a new one, because they don't make parts for this thing anymore - lemme talk to my boss and we'll see what he can give you on a trade in '.
When I first got into this business back in 96, I couldn't stand circ pumps... and hated grundfos. Little did I know that these stupid little things outlast everything I've ever seen since, and are a gem of a replacement circ pump for just about everything around. They also tolerate bad water chemistry better too - but bad water chemistry will still eat them up in the long run too so be cautious. I just pulled a grundfos circ pump out of an old cal spa that had been running for more than 15 years... it finally gave up for the gfci tripping. The internal seals gave out feeding water to the electrical parts - but it still pumped water!
I'm a fan of circ pump systems now, simply because replacing a complete spa pack is so much easier if the spa was designed for one. No bothering with 2" plumbing to a new control system heater from the main pump, just go ahead and plumb the existing grundfos spa pump output directly to the new system heater - (or if it had another brand circ pump, install a grundfos to eliminate call backs) - and wala.. new system operates 24/7/365 without problems.
When you were talking about having difficulty working with the plumbing to the new grundfos pump, well... it's like this. Get rid of and forget everything that was 3/4 in there before. Get about 5-10 feet of 1" fiber webbed flex... and just work it in anyway you can, just be sure that the suction lines stay low. Discharge lines from the pump to the heater can go anywhere they need. Idea is to do it all up without kinking the lines.
Glad to hear of your success with your installation. Now that you've done all this, next time (and hopefully a long time from now) you won't have to work so hard for sure.
Best of luck and thanks for posting your results.