SPLEX.GG has a time-saving "bulk combine" feature that makes it fast and easy to quickly combine thousands of cards to any level(s) that you want.
Here is the bulk-combine in action, 
Steps for Using Bulk-Combine
The video might be fast too follow, here are the step-by-step instructions with screenshots.
Step 1: Go to Your Collection Page
Step 2: Use the Search and Filters to Find the Card(s) to Combine
Step 3: (If Renting) Decide on the Optimum Level for Rental Income Using the SPLEX.GG Market Tools
Details for finding optimum renting levels are on my post How to Increase Rental Returns Using the SPLEX Marketplace.
The short version is, find the card on the SPLEX.GG marketplace and click the star to see the optimum rental levels for 3, 7, and 14 day increments.
For the Pelacor Bandit, for the last 3 days the optimum levels are 9 (gold trophy), 8 (silver ribbon) or 10 (bronze ribbon).
Step 4: Click the Combine Cards Button on the Collection Page
Step 5: Switch from Single-Combine to Bulk-Combine
This is the single combine page view. Press the "bulk combine" button to switch to the bulk combine view.
Step 6: Select Combine Level and Number of Copies to Combine
A. Select the combine level.
B. Enter the number of copies to combine.
C. Click combine.
The bulk-combine feature works great whether you are combining a few cards or thousands of cards.
If you have any questions about how this works or other features of SPLEX.gg, ask here or in the SPLEX.GG discord server.
I hope you found this useful. If you're trying to rent and play from the same account, I've posted some instructions for how you can do that on this article,
How to Rent and Play from the Same Account with SPLEX.
SPLEX.GG has a lot of great free tools that I use almost every day, if you want to learn more you can read about My Favorite Free Tools from SPLEX.