How much will the cost be to convert from 45acp to .460 Rowland on a 1911?
Is the barrel,magazine and spring all that's required?

Be sure your frame is up to the job. I investigated this a couple of years ago and found that the heat treating of frames differs, meaning that some frames won't hold up to the higher pressures.

Me too.  I passed.  It seemed to me that a lot of guys had to fiddle with the conversions too much for my taste in order to get them to work reliably.  Not really "plug and play."  My $0.02.  YMMV.

Every one worries about the frame, yet it is the slide that takes most of the stress.

Not saying you can put a 460 Rowland barrel on a 1918 made Colt, obviously modern guns are the best choice, as mentioned, due to modern heat treating methods.

The slide needs to be of very high quality also.

<---- 460 Rowland fan/owner

Clark Custom Guns offer their "drop in kit" for 5" 1911s... basically a 460 chambered threaded barrel with a compensator and a 24lb recoil spring.  The compensator works and is needed to prevent frame/slide battering.  An addition of an EGW flat bottomed firing pin stop helps too.  Any kit that doesn't "drop in" can be fitted by the smiths at Clark Custom for a small fee (my 5" kit fit and functioned fine). CCG recommends 1911s with FORGED steel frames for their conversion kits.  Although I have heard that the Taurus 1911s frames (even though forged) have failed with the conversion.  CCG used to offer a 460 conversion for Commander length frames but I think I may have purchased the last one of those... which did need to go back for fitting.

Johnny Rowland also finally got his 460Rowland website up and running.  He's offering (last I saw) conversions to 460 Rowland for 1911s, Glocks, M&Ps and XDs.  Don't think his company offers gunsmithng services. His 1911 kits are compensated and the kits for the poly guns are comped or ported.

1911 Kits from either company will run around $300.00
You'll get a compensated 1911 barrel chambered in 460Rowland (1/16" longer case than a .45acp, with the same COAL) and one or several heavier than stock recoil springs but no magazines. 460 Rowland uses same magazines as 45 acp does.

ETA: CCG kit comes with a 2 piece FL guide rod as well... it helps with assembling the gun when using that heavy ass recoil spring. Not sure about Johnny's conversion, although I bet it is very similar to the CCG kit.

I have a Clark conversion on a new Para Expert.  After rebates, I got the Para for $399, so if it cracks, no big loss.  Clark actually has them listed as approved though.  

So far everything is fine, no function problems.  200gr XTP over Power Pistol, at 1400fps.  

Took a lot of the fun out of my 10mms.

I converted a 1911 years ago for .45Super woods carry. We had/have a curious black bear problem at our fishing/hunting cabin right outside of the Nantahala National Forrest. It had a Wolff 23# recoil spring, titanium firing pin and upgraded firing pin spring, etc, etc. I forgot to upgrade the springs in my Wilson 47D's to compensate for the extra slide velocity however. Said slide velocity was faster than the stock 47D springs could keep up and resulted in mis-feeds and stovepipes. Once I changed the 47D mag springs to Wolff 10% extra power springs all ran smooth as butter: very manageable recoil (.45acp+P like), and fantastic accuracy with the 255grain Buffalo Bore flat nosed hard cast lead bullets. The .460 Rowland packs more punch than .45Super with said 255 grain pills at 1100fps. I'm surprised Mr. Rowland doesn't advise putting in stronger magazine springs to compensate for the faster slide velocity... even with the upgraded slide (firing pin & pin spring I'm sure), a 24# recoil spring, and a compensated barrel. Nordic, did you ever experience what I'm talking about???

Now that's cooking! XTP bullets are an inherently accurate too. I love it for a woods load because of that as well for their penetration depth. My .45Super with Hard Cast LSWC's hit harder than an even above average 10mm load too... 255 grains @ 1100+ is nothing to sneeze at...

I've never had the issue you describe, but a big part of that may be the fact that I change out ALL my 1911 magazine springs with Wolff +10% pretty much as soon as I buy them... even my generic 1911 gunshow magazines get the WOLFF treatment before they get used.

ETA:  I also avoid magazines with removable baseplates when feeding the Rowland converted guns.  That's why I like the cheap gunshow mags with their welded floorplates... a quick spring change and they're GTG 99% of the time.

Loaded some generic bulk 230gr JHP's tonight and first load got 1290fps.  

Five shot rested at 25yds 2 3/4".  Three of those were 7/8".  

That is with the stock shitty Para trigger.