OED:
rock-bottom, bed-rock; also fig., the fundamental or lowest possible level, nadir (see also quot. 1866); also attrib. or as adj., lowest possible, unbeatable (of prices, etc.); fundamental, firmly grounded, honest, sound
[1856 ‘OLD COLONIST’ How to Farm & Settle in Austral. 56 This lowest bottom, ‘the rock’ as it is emphatically termed, in reference to its character as a bar to further digging for gold.] 1866 Oregon State Jrnl. 24 Nov. 2/2 A sound democrat, or ‘*rock bottom’, never shrinks from the requirements of his master. 1884 Lisbon (Dakota) Star 10 Oct., Boots, shoes and rubbers in great variety and at rock-bottom prices. 1890 in Barrère & Leland Dict. Slang II. 183/1 Other freight wars, covering much less territory than the present, have gone to rock bottom before any attempt has been made to restore rates. 1902 W. N. HARBEN Abner Daniel 273 See here, I've got a rock-bottom proposal to make to your people. 1904 Georgians 200 Now cool off, an' let's git down to rock-bottom. 1923 D. L. SAYERS Whose Body? vii. 167 There aren't many men who wouldn't be niceto her, and even then, if they aren't rock-bottom she can see through them. 1930 Sat. Even. Post 26 July 14/1 ‘Pay you?.. How much, Angelo?’ ‘The rock bottom is half a million.’ 1935 H. EDIB Clown & his Daughter xlv. 258 By the time she had touched the rock-bottom of misery she had also reached a decision. 1955 D. DAVIE Articulate Energy vii. 69 We are sobered and shocked when the mood reaches rock-bottom. 1977 Belfast Tel. 19 Jan. 7/8 Builders engaged in this work were rapidly reaching ‘rock bottom’. 1980 Daily Tel. 16 Jan. 23/4 In this way, the service can be offered at rock-bottom prices.
