For a beginner D whistle, I highly recommend either Freeman-tweaked (especially his Blackbirds!) or Dixon brass ‘Trad’. Both are very easy to play in tune and both have lovely tones. For a beginner it’s important to have a whistle you can trust and that is a pleasure to play.
Perhaps off topic, but does circular breathing make an appearance in whistle playing? It seems some players just go on and on endlessly whereas I simply do not.
It is done:
https://www.youtube.com/watch?v=ekIIn_BY3e0
Hatao is a member here:
http://forums.chiffandfipple.com/memberlist.php?mode=viewprofile&u=6674
However, I personally have never come across, IRL, anyone using circular breathing. What most players do is choose where they breathe very carefully. The trick is to make it appear that there are no gaps. It’s a bit like the trick of some of the best banjo players, some of whom manage to convey an impression of playing legato, when that is clearly impossible.
Great playing by Hatao, but I was running out of air watching it! 
Especially the flute section, for some reason.
I just happened to toot a bit on my c1980 Generation C just now… wow… I do forget, if I don’t play it for a while, just how sublime it is.
The low octave is big, full, and round yet the 2nd octave is incredibly sweet and easy. I’ve not seen any whistle at any price equal it.
The timbre is complex, yet sweet and clear.
My c1980 Feadog D isn’t as good as that Generation C. Its low range is softer that I would like. But still it out-played quite famous and expensive D’s I tested side-by-side with it, the Feadog’s timbre having that extra something the various new whistles lacked.
I have a few Sweetones lying around the house I bought for my kids in the 90s, and one tweaked. I enjoy them a a quick pick up whistle, but they seem to like a light touch air pressure wise. I’ve also sat in a session where a good player honked on one admirably, but playing a whistle at full volume in tune is actually a skill you learn. (though it is true that some whistles are so out of tune they are impossible to play well.) I’d recommend a Killarny if you can afford them. Or go with a tweaked instrument by Jerry Freedman. They will play like whistles and can stand up to your learning to blow. Since the question was about price, here’s my 2 cents: If you decide you hate the whistle and want to resell you can usually get half your money back, which isn’t bad for a used anything. You are playing a $10 whistle. If you buy a $75 Killarney and decide you’re done after a year and find someone to buy it for $40-50 bucks you are only out $25 for a year’s experiment. I have both the brass and nickel bodies and like them both. Are they the best whistles in the world? Probably not, but I’ve heard them played by great players and they sound good. When we are beginning we seem to think we have to blow hard, which isn’t always the case. This will improve with practice. I don’t know where you are but if you don’t have a teacher around and your internet connection is good, I have enjoyed the Online Academy of Irish Music. They give you a certain number of lessons for free, then it’s $20 a month for all the lessons you can devour. I subscribed to augment my concertina lessons, and, even though I have played whistle and flute for 30 years, I will dig into the flute and whistle sections to learn new tunes.
https://www.youtube.com/watch?v=CuKlbQYf3q0 probably a hohner, preferred instrument for kwela
Just to clarify, I don’t regard Jerry Freeman’s Blackbird / Bluebird whistles as “tweaked” whistles, but maybe others could comment. I think “tweaking” is defined as modifying off the peg mass-produced whistles whereas the Bluebird and Blackbird are somewhere between a mass-produced and a hand-made whistle (and are priced accordingly). I understand that Jerry checks them out before shipping them, whereas cheaper mass-produced whistles might not get that level of quality assurance.
On the intonation question, the intonation is fixed to a large extent by the spacing of the holes on the tube (although players can bend notes in or out of tune using breath control). It’s inconceivable that the intonation of mass-produced whistles would vary greatly from whistle to whistle due to the consistent manufacturning process. However, tone is much more defined by the plastic whistle head, which could exhibit a greater degree of variability (and is where tweaking comes in). It seems much more likely that a “hand-made” brand of whistle would have potentially much greater variable intonation from whistle to whistle, due to the lower-tech manufacturing process, but possibly a sweeter voice with the additional care and attention to detail.
For what it’s worth, I have a Freeman Bleuebird and a Blackbird, neither of which I like that much, but are playable and have good intonation generally. One of them has an unwanted undertone when I play a high D unless I vent the first fingerhole - something none of my other whistles do. I also find them less reliable / stable in the second octave. I prefer my Dixon trad, particularly after I’ve played around with a few different heads, but I’ve also enjoyed playing a Feadog, a whole bunch of Generation whistles, the much-maligned Clarke whistles (Sweetone) and other brands.
Tony Dixon whistles have excellent pop/response smooth playing and in your price range. 