Additionally, building your own solar panel can be even cheaper.
There is a large portion of DIY articles and tutorials on-line you can view, and most consist of the following needed materials to build a solar panel.

1. Tabbing Wire
2. Bus Wire
3. Rosin Flux Pen
4. Extra Solder
5. Solar Cells
6. Copper Wire
7. Pressure Treated or MarineGrade Plywood
8. Pegboard
9. Tile Spacers
10. All Purpose UV ProtectorStain Paint
11. Transparent Silicon
12. Digital Multimeter (checks voltage and current)
13. AWG Wire Cutters
14. Transparent Glass or Plexiglass
15. Charge Controller
16. Deep Cycle Battery
17. DC to AC Inverter
18. Junction Box

To assemble the solar panel together just follow these steps:

1. Decide how large you wantyour solar panel, and cut your pressure treated or marine grade plywoodthat size.
   Drill two holes for the negative and positive connectionwires.
   
2. Cut your pegboard to theright size to fit inside the plywood.
   
3. Use your all purpose UVprotector stain paint to place two coats on the plywood and pegboardseparately.
   
4. Once dry, screw down yourpegboard to your plywood.
   
5. Assemble your solar cellsin series with the tabbing wire, bus wire, and flux pen.
   
6. Mount your solar cells ontop of your pegboard evenly spaced.
   
7. Create your negative andpositive connections with your copper wire (usually red and black) andsolder them to your bus wire, and run them through the two pre-drilledholes in the plywood.
   
8. Lay transparent or plexiglasson top of the entire frame, and apply silicon around the exterior ofthe glass.
   Before you screw the glass down to the plywood to createa tighter seal, pre-drill your holes to prevent cracks from forming.
    Allow the silicon to dry for 24 hours.
   
9. Connect the positive andnegative connections from the solar panel to the charge controller.
   
10. Connect the positive andnegative connections from the charge controller to the deep cycle battery.
    
11. Connect the positive andnegative connections from the deep cycle battery to the DC to AC inverter.
    

After a couple of weeks it would be a good idea to check your solar panels voltage and current to make sure everything is still working properly.
You will also need to maintain keeping the solar panel's glass clean from any dirt that may accumulate overtime.
Be sure to check after a rainy day that no water got inside your solar panel.