You should save a chunk of your budget for a portable projector screen.
The easiest way to solve that conundrum would be to opt for a projector with built-in wi-fi and maybe even some on-board storage too. Are you going to trail a Blu-ray player outside to plug into the projector's HDMI input? You could use a streaming dongle such as a Chromecast with Google TV to get a picture, assuming you can get a decent wi-fi signal in your garden. Set up your projector in the evening for the best results, but the higher your projector's light output level, the more watchable the image will be when there is still some light around. Brightness is also key – particularly if you live in a city or somewhere with lots of light pollution.
