I haven't been to one myself, but I know of a few people who have had very successful wedding receptions in their gardens. It sounds like a lovely idea, as long as you have a big enough garden!
Food wise, if you go for a buffet, wallpaper tables would be perfect for setting out the food. Then you could just hire a few smaller tables and chairs - maybe see if you can borrow from friends if you aren't fussed about everything matching?
You could do the food yourself, or ask people to bring a plate, or hire caterers to come to your house.
Or possibly a BBQ, if you can get someone who is happy to do the cooking?
I think you could make it lovely - set up a little area for dancing with some fairy lights, a couple of gazebos in case of rain, get some bunting up... really nice idea :)
If you end up looking into hiring a place after all, try local football or rugby clubs - they often give good rates.
Hope this helps! Also, if you are anywhere near Bristol/Bath, I know a couple of good caterers! X