The colonnades, the springs and the woods above them are free; what makes Karlovy Vary expensive is sleeping in the spa valley and buying treatments through a hotel, and both are avoidable.
Sleep downstream, walk upstream
Rooms in the modern town around T.G. Masaryka cost a fraction of the same night in the valley, and the walk up the Tepla to the Hot Spring Colonnade takes about twenty minutes past everything you came to see. Do that walk twice a day and you have saved more than the bus fare.
Alzbetiny lazne is the spa without the hotel
Smetanovy sady 1145/1: the town's last public municipal baths, open since 1906, selling swimming pool entry, salt cave and individual treatments to walk-ins rather than only to package guests. The site now runs under the spa5.cz address.
The galleries are the cheap indoor hours
Becherova vila at Krale Jiriho 1196/9 is 80 Kc for the current exhibitions, 40 Kc reduced and 40 Kc for the permanent history display, Tuesday to Sunday 10:00-17:00 - about a quarter of what a spa treatment costs and open when it rains.
Walk out to Svatosske skaly
The marked educational trail from Doubi follows the Ohre downstream to a two-hectare cluster of granite pillars, crossed by a suspension footbridge. Free, about two hours, and the one long walk here that is not uphill through spa woodland.
What a day costs
Colonnades, springs and the forest paths cost nothing. Becherova vila is 80 Kc, Loket castle 145-175 Kc, a spa wafer costs pocket change, and lunch in the modern town is ordinary Czech money. Sleep downstream and a full day of sights here comes in under 300 Kc; book one hotel spa treatment and you have trebled it.