3.c4 would lead to a declined

Budapest gambit, after 3...Bc5 black must have equalised, and that's probably all you can ask of the position...

Freijedo Alvarez,S (2320) - Goldin,A (2540) [A51]

Oviedo rapid Oviedo (13), 1993

1.d4 Nf6 2.c4 e5 3.d5 Bc5 4.e3 0-0 5.Nc3 d6 6.Be2 c6 7.Nf3 cxd5 8.cxd5 Bb4 9.0-0 Bxc3 10.bxc3 Qa5 11.c4 Na6 12.Nd2 Nc5 13.Nb3 Nxb3 14.Qxb3 Ne4 15.f3 Nc5 16.Qa3 Qc7 17.e4 Bd7 18.Be3 Rfc8 19.Rab1 b6 20.Bxc5 Qxc5+ 21.Qxc5 Rxc5 22.Rb3 Ra5 23.a3 Rf8 24.Bd3 f5 25.exf5 Bxf5 26.Bxf5 Rxf5 27.Re1 Kf7 28.Re4 Ke7 29.Kf2 Rf8 30.Ke2 h6 31.Kd2 g5 32.Kc2 Rc8 33.Kb2 Rac5 34.Rb4 Kf6 35.a4 h5 36.Kb3 Kf5 37.h3 Rg8 38.Rb5 g4 39.hxg4+ hxg4 40.a5 gxf3 41.gxf3 Rg3 42.Rxc5 Rxf3+ 43.Ka4 bxc5 44.Re1 e4 45.Kb5 Ke5 46.Rh1 e3 47.Rh7 Kd4 48.Rxa7 e2 49.Re7 Re3 0-1

The b5-idea turned out to have been tested twice btw, which isn't all that surprising since black has similar ideas of encircling pawn d5 in some sidelines in the Benoni, for example Stefan Bücker's Habichd, 1.d4 Nf6 2.Nf3 c5 3.d5 c4!?

Bondick,K - Packroff,H [A45]

corr DDR-cup6 corr DDR-cup6, 1979

1.d4 Nf6 2.d5 b5 3.a4

[ 3.Nc3 b4 4.Na4 Bb7 5.c4 d6 6.f3 Nbd7 0-1 Munyankindi-Walther,E/corr ICCF/WT 1972 (6)] Resignation was hardly forced, but white's position is hardly harmonic. Perhaps black can force the centre open with c6,cxd5 and e6 and use his lead in development?

3...Bb7 4.axb5 Nxd5 5.e4 Nb6 6.Nc3 e5 7.Nf3 d6 8.Be3 N8d7 9.Be2 Be7 10.0-0 0-0 11.Nd5 Nf6 12.Nxf6+ Bxf6 13.Nd2 Bg5 14.c4 Bxe3 15.fxe3 Nd7 16.Ra3 a6 17.bxa6 Rxa6 18.Rxa6 Bxa6 19.b4 Bb7 20.Qc2 Qg5 21.Rf3 Qh4 22.Rf1 Nf6 23.Bf3 Ng4 24.Bxg4 Qxg4 25.c5 dxc5 26.bxc5 Qe6 27.Rb1 Bc6 28.h3 Qg6 29.Rf1 h6 30.Kh2 Ra8 31.Qc4 Qe6 32.Qd3 Ra2 33.Rf2 Qe7 34.Qc3 Qd7 35.Kg3 Ra8 36.Qxe5 Re8 37.Qd4 Qe7 38.Rf4 g6 ½-½