my advice would be to search on craigslist or your local pawn shops. I picked up a teknetics delta 4000 and a bounty hunter tracker iv both for less than $200.
the IV is a great little unit to start. but if you think you will really like this hobby I would suggest starting with something with a digital screen and a depth gauge.
if you search around there are quite a few MDs for around the $200 mark that have notch features, digital display that shows you the VDI numbers (this is the number one thing that has helped me). if you want to go cheap just to give it a shot and you can find this unit pretty cheap then certainly pick it up. you will spend a lot of time digging junk but its a really great unit. before I got a pin pointer I even used this unit as a sort of make shift pin pointer because its light and its really good at telling where the object is just by sweeping over.
im sure if you are brand new that this unit will provide you with hours of fun and hours of digging. but if you really get into it and start having fun then it wont be long at all before you will want to upgrade to something that provides a little more information. so if you are just buying one to tinker around with the kids or have something to do on the weekends, you will be very happy with this. if you think you might be in this hobby for the long haul and your budget is $200 then I would definitely try to get something a little bit better to start off that you can keep for a while like the garrett ace 250 or the fisher f2 or similar. they have lots more features that save lots of time and lots of digging.
all that being said, I gave the IV that I bought to my 12 year old and he loves it. he will stay outside for hours and come back with 100 items he found.
oh and by the way, although this model is pretty darn good at identifying the approximate location of the object, since it has no depth feature and no pin point feature you will definitely want to invest in a hand held pin pointer. everyone has their own opinions on which ones are junk and which ones are must haves. but if you are on a budget like most of us and don't have the money to buy the most expensive thing out there, harbor freight has a CenTech model that's around $16 I think. it works pretty well out of the box and it will help you save a lot of time by being able to pinpoint the exactly location of the object. there are lots of mods you can do to it to make it better that require very little money and very little skill (I wrote one myself in the The Tool Shed forum).
let us know what you picked and how you like it!