Dress boots are for dressage and field boots are for pretty much everything else. I personally think dress boots are the most uncomfortable thing ever known to mankind, so I would buy field boots no matter what.
I have Ariat Challenge Zip field boots and they are great. They are one step above the Heritage boots another poster mentioned. They break in pretty easily. Just be sure to try on a bunch because you can't always go off of your calf and foot measurement alone. I had to try on a million boots before I found some that fit because according to their charts my foot which is pretty small should be accompanied by a smaller calf, but my calves are pretty muscular. I had to get a half size bigger in the shoe part to accomdate my larger calf.
There is more to dress boots than just the really hard dressage ones. For general english riding it is possible (and usually easiest) to just get field boots without the laces, usually considered a type of dress boot. Also, to make it easier to get them on and off it is possible to get ones with zippers.
If you are looking for a relatively cheap pair of boots that look good in both the dressage and hunter/jumper rings then Equi-comfort makes a wonderful boot that fits well and is comparatively durable for other boots in it's price bracket.
Also, imo field boots are ugly in the dressage ring. Those flappy things are just a huge distraction and draw too much attention to a floppy leg. If you are leaning towards doing more hunters or jumpers then go for them, but otherwise general purpose dress boots are much more cost efficient in the long run.
Yeah, I am worried that when I start trying on boots I am going to have the same problem, but oppisite, as you. I have pretty large feet (9 1/2) but they're paired with pretty thin legs.
Have any of you had much luck with used tack stores? I'm going to have trouble affording everything new so I am hoping to find some nice stuff that fits me used.
I had terrible luck with my local tack stores. Partially because they only carry the most expensive of each line, and partially because they just did not have anything to fit me well and they weren't the best at problem solving. It took me going to a tack store in another state to find the size that I needed. Since I can't afford custom boots I tried on a million pairs of boots before finding the right ones. Once you know your size for sure then you can start shopping around for the best deal. I found mine online for $70 cheaper than in stores and they were still brand new. I just needed to figure out what brand I wanted and what size I needed.