Create a simple javascript function to calculate price

Hi,

I'm trying to create a simple calculator for my plan. I have below plans.

50 = $79
100 = $129
250 = $249
500 = $449
1000 = $899
2500 = $1599

Where I have range where user can select a number between 50-3000 and range step is 50;

so if,

user select 50 price $79
user select 100 price $129
user select 150 price is $129+$79 (100+50)
user select 200 then price is $129+$129 (100+100)
user select 350 then price is $249+$129 (250+100)
user select 400 then price is $249+$129+$50 (250+100+50)


so a value can have multiple plans. I need solution in javascript.

Thank you so much