I got the impression (having read more than just the above over the last few months; but by no means is this an authoritative opinion as I've not reached the point just yet of playing with detectors myself) in general that the 305 may be good for starting out or basic coin/relic detecting, but if your more serious about this hobby than the 705 (or non Minelab alternatives if you can find an honest comparison) may be the better option. OTOH the 305 is a good option for trying out the hobby with a chance of being able to reclaim the $ spent if you find the hobby doesn't suit you, as opposed to spending a similar amount to rent one of the more expensive options and come to the same conclusion.
Coming back to the main thread topic, the above website (again: focused on gold > coins/relics) also had a thread from around this time last year on the same topic here: http://golddetecting.4umer.net/t6808-detector-under-1000