You certainly don’t need to pay someone to “convert’ your SketchUp model for 3D printing.
The SketchUp STL extension was created so anyone can export 3D printing STL files from SketchUp.
All you need to do is learn how to create a SketchUp model that’s printable.
3D Printing requires the model be a SketchUp Solid
A Solid in SketchUp is a single Group or Component whose geometry meets the certain standards.
When those conditions are met, Entity Info indicates the model is a Solid Group or Solid Component.
Also notice Entity Info indicates the Volume of a selected Solid.
• The geometry must form a single* airtight vessel.
Like a soap bubble … •No gaps •No holes •No leaks
• No extraneous Faces** inside or outside the vessel.
All Faces must serve to enclose the singular volume of the vessel.
• No stray Edges.
All Edges must serve to support a Face that in turn serves to enclose the airtight vessel.
• No nested Groups or Components.
*A Solid Group or Solid Component may contain one or more separate airtight vessels.
**Best that all Faces are oriented Front Side (white) facing out.