The Main types of Alps that people come across are the following:
The Alps SKCL/SKCM series is the most common found switches that are used on vintage and custom keyboards that use Alps switches.
The SKCL series refers Alps Linear switches that use a different top housing unlike SKCM series switches. These top housings have a hole for the LED would normally be placed.
Most common switches within the SKCL lineup are SKCL Green and SKCL Yellow. SKCL Cream is normally found as a spacebar in some keyboards but they can also be found throughout some keyboards manufactured by Alps.
These switches can feel tactile due to the way that the switch operates and the fact that there is a slight bend in the contacts. SKCL Cream doesn't have this issue as much as SKCL Green/Yellow due to the heavier weighting.
The SKCM series refers Alps Tactile/Clicky switches that share a top housing for both Tactile/Clicky switches. The is one execption being SKCM Brown Alps use their own top housings as they also use a fake contact plate for the tactilty.
There are two main versions of SKCM switches Pine and Bamboo. Below are the examples of both
Pine switches have the slits where the slider interacts with the die of the housing. Pine top housings with the slits are smoother than Bamboo and don't bind as easily therefore, more sought after.
The SKBL/SKBM series of switches uses simplified contacts and contain less parts than SKCL/SKCM due to lack of parts that make up the switch plate.
The best way to think about the design of these switches Matias switches.
The price of Alps switches vary due to the condition of the switches and the type of switches.
The main factor when buying switches is the condition that the Alps switches you are buying are in. Most sellers will rate their switches out of 10 for condition. Now this varies from seller to seller so it's not the best way unless the seller has sold a good amount of Alps. YOu really never going to know how the feel until you buy them.
With Alps switches you want to look for the cleanest switches possible. If you can afford NOS(New Old Stock) Alps switches then go for them if you like the switches.
There is many custom keyboards that support Alps. Two keyboards that support Alps the most is any keyboard that supports Hiney Alps PCBs and 60% that are tray mount. TKLs that support Alps normally use AT101 Keycaps, SGI Keycaps and other standard Alps 101 layout keycaps.
ai03 has also supported Alps with Lunar keyboard that supports Apple keycaps.