We already discussed how to buy bricks but not yet how to acquire a whole set. This part is mostly about auction sites on the net. Of course it would be possible to buy directly from Lego but there are many reasons not to do so: 1. it is expensive (unless you live in the States) 2. the set is not sold any more 3. we would like to have a set with real bricks (with studs).
As usual, the net is our friend. If your dream set is still sold then shop.lego.com tells you its current price in different countries. Usually the States has the best prices. So if you happen to live there or go there occasionally then the best thing is to go to a Lego store and grab it. In the case of older sets like 8860 "Auto chassis" Lugnet tells you its original price.
So far so good, we can start searching on the auction sites. There may be many other sites depending on where you live, we only conside EBay here. If EBay does not have a page in your country, don't worry - you can also register on the site in other countries. For example EBay.de has direct 11 hits for "lego 8860". The good thing is that it immediately lists hits from other countries is well. The results are in the range from "a bunch of dusty bricks" to "unopened original from 1980" with appropriate price tags. A good buy needs a lot of time and searching.
If we decide and did not register with EBay yet, then this is the first thing to do. The best is to register in your own country or in one closeby to avoid customs fees. (This is actually more complicated than that, if you are not sure, ask someone who knows more.) It requires a valid postal address. EBay checks this address by sending a code in a mail. You should do this well before participating in an auction, it does not cost any money. It is also worth having a PayPal account (see previous post).
When everything is set, it is time to start bidding! The recommended strategy is the following: when seeing your dream set, you should first decide how much we are willing to pay for it. (It is advised to learn about shipping costs and other details in advance.) Then you should set an alarm for 5 or 10 minutes before the auction ends and be prepared to be online at that time. When the alarm goes off and the price is still below your treshold, it is time to start bidding. It is still possible that someone else is doing the same, but at least you did not increase the price ahead of time. If you win, the only thing left is to pay and wait for the result.
Really good sets are expensive but there are many bargains, especially if you are willing to make some sacrifice. Remember that Lego bricks are good quality and do not get old quickly. It may happen that you need to clean them, and if there are a couple of missing or broken bricks, they are easy to replace.