Reddit mentions of Jewel Tie 0.06 Carat (ctw) 10k Gold Round Cut Diamond Ladies 3 Three Stone Petite Engagement Promise Ring 1/20 CT - White-Gold, Size 8

Hi again, OP! How is your search going? I had a few more tips and some links to share, if you are still seeking. :)

1. My first advice would be that you not buy anything called "gold overlay" or "plated" or "vermeil." All of those words mean that it is gold, but it's over silver, and it will wear off (often quite rapidly), and the ring will look terrible and cheap. If you can't afford a yellow gold one (which tends to be expensive), go with silver, because it looks just like platinum and white gold to most people, and nobody's going to get out their chemical set and test it. Many silver sets are quite gorgeous!
   
   Here are some examples of silver and white sapphire rings from Overstock (sign up for extra 10% off):
   
   

• http://www.overstock.com/Jewelry-Watches/Miadora-Sterling-Silver-1-6ct-TDW-Black-Diamond-and-White-Sapphire-Ring/5955224/product.html?refccid=NDNIO6VOSNO2ZLCGVXX4BVGGZU&searchidx=2
  
  
• http://www.overstock.com/Jewelry-Watches/Miadora-Silver-White-Sapphire-and-1-5ct-TDW-Black-Diamond-Ring-Set/7885874/product.html?refccid=NORNBALUOSX2CK2L25YUJOAF3U&searchidx=10
  
  What I really like about that last one is that it is a set. A rookie mistake that people make is buying a really pretty ring (like the first one, that has some outer detailing on it), and then it is hard to find a band that will fit with it when you get married. This set is only around $85 for both, and they are made to fit together. So that might be worth including in your search ("wedding sets" rather than "engagement rings"). How it works is you still give her the engagement ring, then when you get married, you already have the ring that you add to it at the ceremony.
  
  

2. Some have suggested CZ stones (cubic zirconia, known by other names such as Diamondite, etc.). These are sometimes now pretty close to the same price as smaller diamonds for a good set, and so only you can tell if your girlfriend will be upset with a "fake" stone or not. Personally I have never owned a real diamond, and I am quite happy with CZ, not only for the price, but because I tend to be VERY hard on rings: when you lose a CZ stone, it's a lot less traumatic than losing a diamond. :)
   
   One option here might be (if you don't think it would upset her) to get a CZ that is in a lovely setting, and then later (if she cares about this sort of thing) you can have it reset with a real diamond for your 5th or 10th anniversary. There are things you can do to get creative on a budget, it what I'm saying. :)
   
   Here's a lovely set in sterling for under $100:
   
   

• http://www.overstock.com/Jewelry-Watches/Sterling-Silver-Princess-Cubic-Zirconia-Antique-Bridal-style-Ring-Set/7308264/product.html?refccid=QJR3GD5QGXDYVTSMZSXJEHRI7A&searchidx=122
  
  

3. Colored stones are another good option, especially if she likes them. If she's never mentioned it, then see #4. To find these, what you want to search is "gemstone rings" - that will get you all the colored ones. Here's a colored stone with silver that comes in a 3 different colors to choose from (black, white, blue), but you can get pinks, greens, reds - the gamut:
   
   

• http://www.overstock.com/Jewelry-Watches/M-by-Miadora-Sterling-Silver-Black-Spinel-or-White-Sapphire-Ring/7260322/product.html?refccid=OOXBXZNPBAAJTE2EFHCJTSQTEQ&searchidx=10
  
  (For the wedding band for that ring, you could do a simple silver band on one or both sides, or what is called an "eternity band" on one or both sides - like this:)
  
  
• http://www.overstock.com/Jewelry-Watches/Icz-Stonez-Sterling-Silver-Cubic-Zirconia-Eternity-Band-Ring/8111022/product.html?searchidx=2
  
  

4. With the surprise element in mind, you could still just go ring shopping with her and get some ideas. I know you don't want to give it away, but just go to the mall in general, stop at lots of places just to look, and make one of them a ring shop. You don't have to buy from there at any point, this is just an expedition so you can get a feel for what sorts of rings she likes (I doubt she will have any trouble letting you know!). :)
   
   
5. Finally, if she really wants gold, and she really wants diamond, a clever search can STILL net you things that will work! Here is a 10k white or yellow gold with real diamonds for around $100:
   
   

• http://www.amazon.com/Carat-Diamond-Ladies-Engagement-Promise/dp/B00OP5K92A/ref=sr_1_3?s=apparel&ie=UTF8&qid=1417975590&sr=1-3&keywords=gold+band+solitaire
  
  Good luck to you!