I worked for a local company that supplied aftermarket parts for everything. I mean engine parts, electrical, undercarriage, filters, oils, hydraulics cylinder seal kits etc. The undercarriage was so cut throat. Sometimes we could supply undercarriage spread over 3 or 4 companies. Like ITR, TTP, Equipment Sales, KTSU. Only to find out that Case, John Deere or Cat had beat our price with OEM parts. We were making anywhere from 3% to 10% on undercarriage. It was basically a way to get business in the door for other sales.
If I needed undercarriage my best advice is shop around everywhere. Even OEM dealers as some ( at least here in Ontario) will sell undercarriage for competitors machines. The one factor that makes a huge difference is shipping. Undercarriage is heavy and shipping costs can add up quickly. Some aftermarket suppliers will ship free after a certain dollar value. OEM and ASftermarket may ship free but FOB their location. You don't want to order undercarriage from a supplier only to find out you get a $500-$1000 freight bill. So when you order ask about any shipping costs.