Not expensive
inexpensive, low-priced, medium-priced, reasonable, within reason, modest, inexorbitant, not excessive, not dear, average, nominal, at par, usual, inconsiderable, marked down, at a bargain, half-price, reduced, worth the money, relatively low, of small yield; see also cheap 1, economical 2.
Antonyms expensive*, dear, exorbitant.
Not extreme
temperate, measured, judicious, unexcessive, restrained, considered, reasonable, unextreme, balanced, equable, easy, average, steady, even, deliberate, calm, cool, mild, clement, gentle, unimpassioned, low-key, dispassionate, cautious, sober, prudent, sound, controlled, regulated, modest, conservative, medium, midway, within compass, within limits, striking the golden mean; see also calm 1, conservative, mild 2.
Antonyms immoderate, intemperate, extreme, excessive.
Not radical
centrist, middle-of-the-road, tolerant, nonpartisan, unopinionated, undogmatic, not given to extremes, nonviolent, neutral, impartial, respectable, middle-class, preserving the middle course, compromising.
Antonyms radical, extremist, fanatic.
Average
middling, modest, fair, mediocre; see common 1.
Not indulgent
temperate, restrained, sober, sparing, abstemious, frugal, self-denying, abstinent, unindulgent, self-controlled, disciplined, careful, teetotaling, on the wagon*, straight*, sworn off*; see also restrained, sober 3.
Antonyms self-indulgent, intemperate, wasteful.