You could check the RDR2 Wiki to see what vanilla prices are. For instance the Cattleman in the regular game is $50, the mod should make it $100. Regular revolver ammo is $1, the mod should make it $2.
I'd check your vfs.txt log in your RDR2 main directory. If the files are loading correctly, it should have some lines like this:
2021-07-20 21:18:08 INFO d:\gtav\vfs\vfs\vfs\rdr3\customcollection.cpp:482: Global full replace: addonDLC:/hardcoremode/catalog_sp.ymt
2021-07-20 21:18:08 INFO d:\gtav\vfs\vfs\vfs\rdr3\customcollection.cpp:482: Global full replace: addonDLC:/hardcoremode/lootconfigdata.meta
2021-07-20 21:18:08 INFO d:\gtav\vfs\vfs\vfs\rdr3\customcollection.cpp:482: Global full replace: addonDLC:/hardcoremode/loot_table_reward.meta
2021-07-20 21:18:08 INFO d:\gtav\vfs\vfs\vfs\rdr3\customcollection.cpp:482: Global full replace: addonDLC:/hardcoremode/loot_table_ped.meta
2021-07-20 21:18:08 INFO d:\gtav\vfs\vfs\vfs\rdr3\customcollection.cpp:482: Global full replace: addonDLC:/hardcoremode/loot_table_itemgroups.meta
2021-07-20 21:18:08 INFO d:\gtav\vfs\vfs\vfs\rdr3\customcollection.cpp:482: Global full replace: addonDLC:/hardcoremode/loot_table_container.meta
2021-07-20 21:18:08 INFO d:\gtav\vfs\vfs\vfs\rdr3\customcollection.cpp:482: Global full replace: addonDLC:/hardcoremode/loot_table_passthrough.meta
2021-07-20 21:18:32 INFO d:\gtav\vfs\vfs\vfs\rdr3\customcollection.cpp:482: Global full replace: addonDLC:/hardcoremode/pedhealth.meta
Make sure you're also using the most recent version of Lenny's Mod Loader, and the most recent version of Alexander Blade's ASI Loader (just updated yesterday) or LMS's ASI Loader.
Unless you have another mod installed that uses catalog_sp.ymt in your "lml" folder, it shouldn't be overwritten by anything.