Honestly, if you are looking for rims for your Mustang, the Apex rims are quite reasonable for the high quality and fitment. I have purchased 4 sets over the past 4 years ( two different cars ) and was never able to get in on a group buy. Most companies never do group buys, so it is nice that Apex does work with TMO and others to offer this option at times, but I needed rims when no programs were in place. After doing my due diligence I found out the key things I was concerned about ( fitment, hub centric, sizes, quality, fair pricing, solid supplies, knowledgeable reps, etc. ) were not an issue at Apex. I was very tired of hearing from Reps that something might work, or that there were no squared set up options available? The guys build rims to our necessary track specs , at a price similar or lower to other rims and they are available for service, questions, etc.
If you need rims, get them so you are not scrambling at the last minute and if you can acquire during a group buy, great , but keep in mind the regular price is quite solid. Another thought is there is usually a Christmas/New Years sale price on many rim sizes at the end/beginning of the year, so that might be your option?