I lived out there for a couple of years, Loads of riders that are friendly, will put you up if you need a place, spots are awesome and weathers good depending on what part of australia you go, £3000 should be fine but flights will be around £600+ return from there, if your under 25 sta do awesome deals, accomidation is not cheap however if you are just planning on staying in hostels your looking at around $120 bucks plus a week for accom, renting camper would be cheaper, the conversion rate on the aussy doller isnt that good £1000 will give you about £1500 something aussy dollers hope this helps, bondi has some sweet spots im there next year so if your around hit me up and il come ride and give you a place to crash
Also Food is alot more expensive but petrol is dirt cheap and goes up and down in different areas was about $1.90 for petrol in December when i was there
Also again, you can only have a working visa once, so if you get one of those you will be asked to have $1000 for every month you are staying and will have to provide this with proof, alot of the time when just on a visiting visa you will be asked to produce proof you have the funds to travel in australia and will be refused entry if you dont have enough, Do some hard research into it and make sure what visa is right for you