You can do what you do. First the boxes are text and you don't get the text by the .Text attribute. Also you want to have numbers and not text so you have to convert them by the Value() formula before you can add them together.
So do this:
Sum(Value(TextInput2_2.Text),Value(TextInput2_3.text),etc.)
Surround this by a text() formula like:
Text(Sum(),"[$-en-US]#.#0")
Or do this to get the same you have, but I would take the first.
"$" & Text(Sum()) & ".00"
For the textboxes.text you do like this:
Text(
Switch(Slider1.Value,
1,1517
,2,2925
,3,6740
), "[$-en-US]#,###.#0", "$-en-US")
And rename your boxes to a better name like V1, V2, V3, etc.
Hope this helps.
Paul