I really like the rx7's as they are really light, but they are fragile.
To put this in perspective, your single turbo 7 will put down about 450 rwhp. My supra on stock twins with a fmic and a fuel computer put down 449 rwhp and 468 ftlbs.
I have been seriously looking at the different paths for going single.
here are the extreme ranges for you...
turbo kit -
used - $2k (log manifold, etc)
new - $6k+ for big singles from WOTM, SP, RPS, etc
intercooler -
$1k - $1.5k
clutch-
$600 - $2 or 4k
exhaust - $450 used to $1100
Fuel computer - $200 (used S-AFC)
you could get away with just doing this, or you could add an AEM, or a VPC, or the new PHR computer. And $2k for the fuel system to make serious power.
And from here, the sky is the limit. CAMs, Cam gears, intakes, etc...
Good luck. Its a slippery slope.
Matt