Amazon has them at 1.44 per pound. This link allows you to "set up a subscription" for 25% off. 1.08 per pound on the first order:
Great River Organic Milling, Whole Grain, Rye Grain, Organic, 25-Pounds (Pack of 1) https://www.amazon.com/dp/B0049YM8XU/ref=cm_sw_r_u_apa_glt_fabc_Y7GVJC0KHKQ5BYEX57C2?_encoding=UTF8&psc=1
I also used these with no issues. Just cost more then the whole oats i use now.
Great River Organic Milling, Whole Grain, Rye Grain, Organic, 25-Pounds (Pack of 1) https://smile.amazon.com/dp/B0049YM8XU/ref=cm_sw_r_apan_glt_fabc_QQ3G5P9AB1Z180BBXG1E?_encoding=UTF8&psc=1
Yo check this one out. I've been using that brand for a while now, nice and clean, intact berries, etc. And with prime shipping runs a little bit cheaper than the link you posted.
That is very healthy growth. I know this is you first time, but I highly recommend buying a 25 lb bag of rye berries off of Amazon for $40 (not the best price but the Great River Organic Milling stuff is really clean and high quality. Then you could set aside 1 of those jars as a "grain master" (I know you are doing cakes, but still). You just use a rye berry prep tek and make a dozen quart jars.
In a still air box, or in a clean room, or using the oven-on stove method, or with a flow hood (if you got the $) -- just scoop a heaping tablespoon full of the colonized PF cake and quickly open the jar lid of prepped and sterilized rye grain and dump in a spoonful of each. You will find grain 2 grain (with proper sterilization techniques) to be very quick and easy way of multiplying your yields. Then just go to a Dollar store and buy a bunch of $1 6 quart totes (shoe boxes) and once the Rye grain quart jars are colonized, dump in 1 or 2 quarts of the colonized rye, then 2 quarts of coco coir and vermiculite hydrated in a bucket with boiling water and let to cool for an hour (you know you have the right moisture amount if you squeeze a handful and water pools between your fingers but doesn't stream down and drip everywhere).
You can drill a few holes in the top (3/8" works or 10mm) and cover those with surgical tape, then lay a small sheet of bubble wrap on top (with about 1/2" to 1" of space left around the sides of it on the coir. You shouldn't even have to mist or anything -- after about 2 weeks you should be able to pick up the bubble wrap and start seeing pins (give or take a few days obv.
My "shoebox tek" is kind of a hodgepodge of other teks and the bubble wrap really just keeps more moisture trapped on the top so you get more top and let side and bottom pins. I know cakes are tried and true newby tek, but the difficulty of moving to shoebox monotube is not high (and honestly the bulk substrate and fruiting stages don't require complete sterility, by the time rye grain is fully colonized it's pretty hearty and can fight off MOST contams).
I'm going to do another shoebox tonight, I'll try to take some photos and post a tek on here if anyone is interested, I also collect and dry out horse poo from a horse trail near my house which I add a bit of to my coco coir before dumping the boiling water over it as well, but straight coco coir and vermiculite work great on their own.
I get mine on Amazon through Great River Organic Milling. It's $37.81 for 25lbs, if you can't find an individual to buy from.
Yup, this is the grain I use. Great River Organic Milling, Whole Grain, Rye Grain, Organic, 25-Pounds (Pack of 1) https://www.amazon.com/dp/B0049YM8XU/ref=cm_sw_r_cp_api_glt_i_BAQ6TBPPE5M1EZDF0135?_encoding=UTF8&psc=1
rye on amazon $37 for 25lbs.