You can trade at a bucket shop tax free in the UK. It is called spread betting. www.ig.com
See https://www.trade2win.com/threads/uk-tax-and-spread-betting.230466/
Esignal classic delayed is $50 a month, then use www.mechtrading.com qcollector to get the intraday futures data to a CSV file. Qcollector can be set to continuously update the CSV file.
Your web app can control qcollector with an API.
http://mechtrading.com/developers/index.htm
AMD APU (CPU and GPU combined) will run four monitors at 4K for less than an intel chip that will run three monitors if you have the right motherboard. No need to upgrade the motherboard when new AMD chip is released.
www.deriscope.com is a free excel add in to get free stock and futures data.
www.interactivebrokers.com have an excel link.
www.marketxls.com is a paid service