What size are you currently running?
If you can get the R45B compound it will hold up and little better and does not over heat as easy as the older R45 and R45A compounds. On the R45B the construction of the sidewall was improved, and they are not as temperature sensitive as previous iterations.
I have been running the hardest compound R55A at the track events and drivers schools. We tend to get a large amount of track time so I something that handle a lot of heat cycles.
The main thing with the slicks and also most R compound tires is that the different compound ratings have that much more "stick" then others. It is just how fast it gets up to temp and how wide the temp range the tire can handle.
Who are you looking at ordering the tire from? On the RR slicks the prices are mostly fixed so shipping can be the greater cost. I have been order mine from Hoosier Tire North in Rogers, MN
http://www.hoosiertirenorth.com/
They get a truck in from the factory every Thursday and then I normally get my set on Friday or Monday via SpeeDee Delivery. I only have to pay shipping from Rogers, MN. Since they are shipping across state lines they are not charging sales tax.
A other place to look is the Hoosier discontinued tire page. You get free UPS ground shipping ($7 processing fee for the total order) for all on-line orders from this page. This inventory changes a lot so you may want to keep an eye on the site. They don't have too much on there now unless you have a old Grand Am Rolex Series car you want to run.
https://www.hoosiertire.com/discontinuedtires.htm