Danny,
Check out Fine Firearms in La Mesa....A used Mossberg or 870 may only cost a couple hundred bucks....Make sure it's a 12 gauge too (modified choke if fixed)....As much as I like 20 gauge guns, the new shells restrictions will make a 12 gauge good for every kind of game, including waterfowl....Start saving money....It's a long and winding road of buying gear....
Ask lots of questions about what you need.....It will save you money in the long run.....Lots of used stuff out there....Check out swap meets, Goodwill, Craig's list, etc.....What sizes do you wear?