Depends on who you use. An initial meeting is usually free. However moving forward I pay about 1.45% all in. This includes the services of my IFA (quarterly reports, half annual meetings, and email/telephone support, the use of a Platform (I use Ascentric), VAT and other bits a pieces. Sounds a lot, however I have seen a growth in my fund of over 5% over the last 12 years (after deductions) - with a low/medium risk profile. So it's certainly washed its face
If you want to spend the time doing the research then you can just set up an account and buy/sell your own investments, which is a lot cheaper, but I had neither the skill, time nor patience to DIY.
BTW the max you can put into a SIPP during a year is £40k. Plus donot exceed the £1.05m life time allowance limit (indexed linked) simply because it's then subject to 55% tax. Nice problem to have
Hope this helps.