That 120 ultra speed is probably increasing to 300 or 400 soon. DslReport mentions a speed bump for unknown areas on March 1st.
A downgrade should keep you at base 100 as long as your computer/router/cables/net adapters support it.
Here are the usual rates . Hopefully you get it figured out in your location.
100d or 200d - $45 with own router
120d, 300d, or 400d - $70 with own router - $50 ultra install fee
940/35 gigabit - $105 - $200 install fee
100d or 200d - $65 with own router
120d, 300d, or 400d - $90 with own router - $50 ultra install fee
940/35 gigabit - $125 - $200 install fee
Knowing spectrum it would be tough to get them to let you stay with ultra and get moved down to $70. They probably consider you on a old promo that can't be changed.
What month is your ultra promo suppose to end if you already had it for a year?