Where to get a modestly priced 5 volt Linear Power Supply?

Up to $100. I understand the iFi wallwart is switching, not linear.

An ebayed 5V/2A Chinese Zerozone LPS is a bit more @$130 including shipping.  I've had great results with this powering a JCAT Net Card Femto in my music server.

You could also try a supply house like Mouser, which carries a lot of different products. Type in Mouser and linear power supply. You'll be taken to a page where you put in certain parameters, like output voltage. There seem to be an array of products. Obviously, you want one they have in stock. I've bought parts through them- fast shipping and not overpriced. There are also high quality lab grade ones, used, but that's probably overkill. 
Depending on application, some of these supplies are, at least according to audiophile designers, not robust enough to power a computer run as a server. The audiophile versions can be expensive. If it is not a critical application, one shortcut is to look for a bench supply with a large toroidal- I found one, a little more money than your budget, with three channels of output, two with variable voltage and current. I can post an article about it- got it through Amazon, and though it looks virtually identical to another brand, it was better build. I use it to power a small DSP and a couple other non-critical units to eliminate the switching supplies. 

The iFi unit is not lps correct but also is vastly different to your common garden switching ps walwart.
As I said depends on your budget, just my results I was sharing.
Good luck in your search! 

Lots and lots of 5v lps on the Bay

This one from Jays Audio is likely not the worst of the bunch for sure and price is fair,



https://www.ebay.com/itm/DC5V-USB-15W-2-0A-Linear-Power-Supply-Dual-Output-CAS-XMOS-Raspberry-DC-reg...