Ace Hardware has a 4" silicon carbide C/F stone (~$5) that seems to be identical in looks/performance to Norton's 6" 'Economy' stone found at Home Depot (~ $7), also SiC. Either of them works very aggressively on all but the most wear-resistant steels (S30V, etc.).
If using S30V or similar, I'd go with a diamond hone. A 'credit card' hone from DMT would be my first choice (available in C/F/EF grits). Those can generally be had for ~ $15 or less, per hone. The finer grits, and especially the EF, can work quite well on simpler steels also (1095, Case CV & Tru-Sharp, 420HC/440-series, etc.).
Pretty sure Norton also has more 'portable' versions of their India stones (aluminum oxide), maybe down to pocket-size. Don't have one of these, but I'd bet they're good also. All should be less than maybe $20 or so; maybe significantly less.
David