  This is the first in a series of papers, where we introduce and study
topological spaces that realize the algebras of quasi-invariants of finite
reflection groups. Our result can be viewed as a generalization of a well-known
theorem of A. Borel that realizes the ring of invariant polynomials a Weyl
group $W$ as a cohomology ring of the classifying space $BG$ of the associated
Lie group $G$. In the present paper, we state our realization problem for the
algebras of quasi-invariants of Weyl groups and give its solution in the rank
one case (for $G = SU(2)$). We call the resulting $G$-spaces $ F_m(G,T) $ the
$m$-quasi-flag manifolds and their Borel homotopy quotients $ X_m(G,T) $ the
spaces of $m$-quasi-invariants. We compute the equivariant $K$-theory and the
equivariant (complex analytic) elliptic cohomology of these spaces and identify
them with exponential and elliptic quasi-invariants of $W$. We also extend our
construction of spaces quasi-invariants to a certain class of finite loop
spaces $ \Omega B $ of homotopy type of $ S^3 $ originally introduced by D. L.
Rector. We study the cochain spectra $ C^*(X_m,k) $ associated to the spaces of
quasi-invariants and show that these are Gorenstein commutative ring spectra in
the sense of Dwyer, Greenlees and Iyengar.
