Just search a price comparison website. I know a good one but you'd have to live in central europe. Usually you can select the size and features you want and you get a list of monitors that fit the bill.
For mainly office use I would suggest Montiors with A-MVA panels. They have stellar contrast and great viewing angles and they are cheap. TN Panels are the best for gamers. AH-IPS, PLS, IPS are really only good if you buy the expensive ones in the low end they are worse than either MVA or TN with no true strength and poor contrast and washed out colors.
I can find plenty in the 100€ region so 100-150$ should be easy to find.
www.prad.de is a good source of reviews but in my opinion there isn't to big a difference in the low end. Look for features that you like, like height adjustment options and overall looks.
BenQ GW2450HM or its smaller brother BenQ GW2265HM
MVA is the best for office use and with the contrast the retina display might look washed out next to it. At about arm lengths distance the resolution on my 23" 1920x1080 looks just fine next to retina. Barely noticeable the pixels.
21" is better if you need to put it closer (if there is not enough space on the desk), otherwise get 23". They cost about the same and you can always put 23" a bit further away but it is often nice to have something bigger.
