This is the list of everything in the store;
On the left hand side TOC select “SSD Caddies”. You would order the 15mm or 7mm caddy depending on the height of your SSDs, probably 7mm. I think $30 is obnoxiously pricey though, even by 45Drives standards. If you have a 3D printer you can print your own. I have a few low rent solutions here Convert Drive Cage to 2.5" Drives - #8 by DigitalGarden and here HL 15 - Workstation & Shared Data storage - #11 by DigitalGarden.
And on the TOC navigator at the bottom is “Enterprise Drives”. Select that and you will see the drives they have for sale. Again, though, they’re not going to be competing on price. If you want everything to show up in one box or from one source for warranty issues I guess that is a thing (I think 45HL do provide concierge RMA help with no questions asked as part of the drives they sell, but maybe that’s just on the enterprise side). But for me, used drives off of ebay or one of the used server parts retailers involved in decommisisioning data centers has worked out fine for RAID. There may still be a lot of inventory from chia miners. Just look for anything sus in the SMART data, but most drives are going to fail in the first few weeks or near end of expected life, not usually in between from random failures or abuse.
I’m not sure why sales didn’t respond to you. Since the drives would ship separately from the chassis, you might not get any shipping discount trying to combine that explicitly with the HL15 order. Just place two separate orders.