Where can I have and cater a wedding reception in Portsmout, VA without going over $900?

Check your yellow pages under 'catering' and get some quotes. I think they would have to know how many people you intend on having. So get your 'ducks in a row' before you start asking them.

If you have a big enough property, cater it yourself and get your friends to do the cooking.

I agree with what tickle has said. In addition, maybe there is a town hall, church or club house/building, or other facility available to the public where it would not cost as much to rent out the room or rooms.

Just another thought. Sometimes parks will have buildings where receptions can be held.