I won't get into the stuff about talking down the Walmart or Radio Shack detectors in general. Some people get confused because they are name brands. Bounty Hunter, I think. That has already been said by some, in other similar threads and, I don't think is really the point on the subject. Other than the customer service that you can expect from mass retailers like that. What is really the issue is the level of quality and features that the $50 machine would have. Very basic. These are machines that are made by brand name manufacturers, specifically for mass markets and are designed as such.
Go to a place like Walmart where they sell everything from jars of peanuts to Furniture and Blue Jeans... and what can you expect someone to know about Metal Detectors. Have a problem with your detector and are you going to be comfortable that someone will know how to resolve your issue or will they just say, Oh, we can exchange it but we are out of stock. It will take 3 weeks before we have more.
On the other hand, go to a place where they sell nothing but metal detectors and associated supplies and what kind of service do you think you will get. For that reason in itself, I would start by looking at a regular detector dealer.
From there, I would also recommend spending a little more for a machine that has better features. You aren't talking an issue of a quality detector, not because it is Walmart or Radio Shack but, I think because of the fact that it is $50. How much can you expect, feature wise for $50. If you were buying this for a young child who just wants a toy and might not be mature enough or dedicated enough to warrant a more expensive machine, that might be an option. I would consider these $50 machines as TOYS not serious detectors. Like I said, not because of who sells them but just the basic level of the machine.
That said, I would recommend, as others have, going with something more advanced. Depending on how much you have to spend and how serious you are, you can probably get a reasonable detector for around $150. Actually, I would start more around $200 and get something like the Ace 250. I am not familar with that myself but I have read many recommendations on that model. I thought of one myself, as a second machine. However, I personally own a White's XLT. It is a much more expensive machine that while is good, I don't know that I would recommend. Reason being the dramatic difference from what you were saying about $50 and the cost of over $800. Big difference. Keeping more in line with what you might be looking for, I would go with a White's Prizm detector. There are several models that range from around the $200 range up to about $500. One that I saw and liked a lot was a Prizm IV which was quoted to me for $360. Being that I am already a White's user, I was leaning more toward that for a second machine than the Garrets Ace 250. Look at
www.whiteselectronics.com and check out the Prizms. Note the features that are available on the models and start by familiarizing yourself with what they will do for you. Then, determine what you would want and what would be helpful for you. From there, you could look at the line from Prizm I and Prizm II to a Prizm V of that would fit for you. Add in the Garretts 150? and 250 and see how those match.
Those are some of the machines that I have heard good stuff about. I really think you would be better off setting yourself a little higher and making a bigger investment innitially. Like was mentioned, it is a strong possibility that you will go out and spend $50 on the lesser machine, then about another $100 on sand scoops and digging tools and such then find, in a few weeks or couple months that you want something more and will find yourself spending the $250 or so anyway.