Rob over at Heartwood is doing a very good series on marking gauges. I can't add much other than price doesn't always correlate to functionality. I've several very beautiful marking gauges that were close to or over $100 USD that are unusable and several very plain and cheap gauges that I use often.
If you haven't, go read Rob's posts, there is a lot good information in the three current posts on marking gauges. About all I have to add are a couple of links to gauges I've found usable and cost effective.
One of the best gauges is a Ryuma screw lock from Tools from Japan that cost around $13 USD. A step up in quality and a little better functionality is also from Tools from Japan, a "Kegaki" double bladed mortise gauge for about $125 USD. The Kegaki is very similar to a Kinshiro gauge which will cost around $320 USD if you can find one for sale. I have both Kagaki and Kinshiro gauges and the biggest difference between them is the Kegaki is machine made where the Kinshiro is truly a work of art.