Here's some possibilities:
AT&T 2462 2.4 GHz DSS 2-Line Cordless Phone with Answering System, Speakerphone, and Corded Basewhich is the older version of this
AT&T E2562 2.4 GHz DSS 2-Line Expandable Cordless Phone with Answering System and Corded Basehere's another possibility:
Panasonic KX-TG2740S 2.4 GHz DSS 2-Line Expandable Cordless Speakerphone with Answering System and Caller IDwhich uses this handset:
Panasonic KX-TGA270S 2.4GHz ExtensionI didn't post prices, because these are mostly older models. Truly hot deals have happened on these phones, but I'm having trouble finding a blazing deal that's current. My strategy would be to check Ebay....get an older model that someone else stocked up on. Probably don't want to risk getting used, make sure it's NIB (new in box) .... because parts, batteries and such might be old, and could be expensive and troublesome to find replacements...thus driving up the total cost.
Most of these systems won't come with 3 stations by default, you'll have to buy extra handsets....but Ebay might have a good "package deal"
Anyway, read the reviews, phones differ greatly in quality, you may not be happy with the absolute lowest cost model. If you can give us a better idea of what "low cost" is, that will help narrow things down.
I don't know if any of these models do the "treed message" thing. You may even need a separate unit for that. Maybe computer software could do the job. I'm really no expert on phones. Just trying to help get things started.
Another thing to consider, this system will be used in your church, home? Was a little unclear. Anyway, if the building is large enough, or there are a lot of walls, or the walls are made out of shielding-type materials....you could have quality issues. You may need to pay attention to frequency and signal range.
Hopefully this gets you started. You might try searching for something like
CODE
cordless phone "2-line"
to find more possibilities.