Since most companies don't make holsters to fit the old large frame New Service, you're going to be limited as to availability and "economical" may not be possible.
There are several options. If you'd like a military style flapped holster, El Paso Saddlery and Pacific Canvas & Leather make replicas.
The El Paso is a absolute top quality replica, the PC&L is made in China and is of fair quality.
For a commercial holster, again El Paso Saddlery offer a variety of both modern CCW and 1920's and 30's period type holsters that would be appropriate for the New Service, are top quality holsters, and not as expensive as some others.
Among the period holsters that would be excellent are the Tom Threepersons, 1920 Crossdraw, #2 Thumb break, 1930 Austin, #5 Patton ,and the 1917 military.
El Paso Saddlery - Holsters
Chinese made replica US military holsters:
Pacific Canvas & Leather Co. Inc. | www.pacificcanvasandleather.com