I'd suggest looking at dry hiring an excavator for the more specific digging and drilling jobs.
Just as an example.
http://www.proexcavationsplanthire.com.au/rates/ Remembering you also have to float there and back + fuel.
If your going to buy, look at it as a long term purchase, as if something goes bang it could cost you a lot of money and you may need to keep it for a long time to get your value from the purchase+repair. I'll also add while the market is flooded with cheap secondhand gear due to the economic slow down in recent times, the first thing most contractors do when short of income is skimp on regular maintenance. Something to keep in mind, there are good buys out there. I just brought a 3 year old machine with 200 hours on it for 10K less than a new one.
