I'm one that HATES to constantly replace equipment. I am new to this, and have just ordered my first machine -- the Minelab Etrac from New England Detectors. I did my research, I've spent time in the field with a gentleman that has an Etrac, and I loved it! I don't live close to him anymore, but I saw what that machine can do, and I went with him enough times to know that this is a hobby I am not soon to put down. So I opted for a better machine than the entry level ones.
Just my suggestion, but if it is possible, I HIGHLY recommend spending some time along side an experienced person before ya start this hobby. Ask them questions, see if you like the machine they are using, and if you like the hobby in general. I think detecting is one of those things that you will either love it or hate it. If ya love it, dive in a get the best machine ya can. If ya hate it, you will know after only a short amount of time afield with the experienced person, and you won't have any money invested at all. Granted, I know it isn't always possible to have that experienced person around to go with, but if ya do, I believe the information they can give is very valuable. Its just like the info you get on this forum, only its in person!!
Just my .02