It is very possible to print hollow objects, in fact that is one of the unique attributes of 3D printing. Not only can you print hollow objects, but can have a separate manifold meshes printed inside a larger mesh.
I'll venture a guess that your issue is with Normals. If the normals are not oriented correctly, it can confuse the printer software as to what is inside and what is outside and make part of your model solid where you intended it to be hollow.
If you have Blender at your disposal, it can help.
Load your model into Blender. (Export it to a different format if you need to.)
First thing you want to do is remove all the duplicate Vertices which is common for imported meshes.
Go into edit mode by hitting
{TAB} and then select all the vertices with the
{A} key. (Note: The
{A} Key is a Toggle That both Selects all and Deselects.) Once you have all Vertices selected, hit
{W} and then choose
[Remove Doubles] from the pop-up list.
A nifty trick in Blender is being able to actually see the orientation of the normals by making them visible. Hit the
{F9} key and then on the far right hand side, look for the
[Draw Normals] Button. Click that and your normals will be visible as light blue lines. (They may be too short to see them well. If so, just increase their size with the
[NSize] slider just above the
[Draw Normals] Button.
Try that and export it to a .STL file and see how much it costs.