I think I recall back on Discord a while ago, there was a guide for the Gems, older ones so Apatite, Labradorite etc, and had a small pricing guide to them. Some of the newer dyes may technically go for more but it also depends on how much someone is willing to spend on them. 

Anymore as of late, this is my own opinion and to be taken with a grain of salt, I simply price my gems at a lower price just to get rid of them, same with my regular old dyes but nowadays I much rather just sit on them and keep stock piling them.

The most you could do is put up some of your items and just say hey, I'm looking for Bits or Ingots but I don't want a ridicuously low price for the batch either and see if anyone offers anything.

Earlier, I managed to sell 23 and 25 lassos and whistles respectively, I put down a flat price of 30k for them both and someone bought them up. If they don't sell or get a good enough offering that you may like, you can just simply keep the items and sit on them. You could see what others are offering for and go cheaper or not, that is up to you but I do not believe there is a right nor wrong way to go about selling stuff.

In my opinion, a lot of things are selling for pretty hefty prices these days. I sell the basic dyes for 1k bits each, and any other seasonal ones, excluding the current ones, I would sell for 2500 bits. If I sold any current season dyes, probably 5k a dye, as they are the current sought-after dyes. 

In reference to gems, their value was discussed and I have used it since at 2k bits for Labradorite, Saphire, Quartz, and Emerald and 1500 bits for Garnets, Apatite, and Rubies. I am not selling new gems yet as they are new and hard to come by but because they are those I would easily sell 5k bits each. 

Tack, I don't sell for any more than it's worth. The average tack is a few hundred bits in store. Unless dyed or encrusted, you can add value of the dyes and gems, and the cost to dye/encrust them. For exampled a white saddle pad is 100 bits. Dying it costs 75 bits, and add whatever you value to the dye you are using. Say a basic purple dye, I sell those for 1000 so I would add that to the price. Encrusting costs 2 ingots and say I used rubies. I would add 1500 for the ruby and 500 for the 2 ingots (ingots sell best at a rate of 250-500 bits per ingot) so that is like 3715. You can round it, maybe 4k bits. Depends if you wanna profit or if you just want to get rid of it, ya know? 

Special tack costs ingots, like the strawberries and cream right now. You can sell those for the same or cheaper ingot prices or the rate of bits. So those saddles are 50 ingots or 15k bits if you sold at a rate of 300 bits per ingot. Does that make sense? 

I don't usually sell treats myself as I like to use them and have a hard time finding them but I would probably sell basic ones for 1k bits, or if I cooked some treats in the craft room maybe 1200-1500 bits. Whistles and lassos maybe 2k bits. 

These are just examples of how I sell stuff, and everything always sells quickly and easily for me.