Though both are correct, I would agree with @rhetorician's assessment - the flow is better without the extra word. Brevity is generally best when making a point; even more so when you're simply linking up verbs. The extra 'to' does not add anything to the sentence; it merely sits there, taking up space on the page and on the eyeball. I would also suggest alternative to your options:
What I would like is to buy it.
This option infers the 'to do', and would be much more acceptable in American English than British. That's not to say it would be incorrect in British English, but it is more of an American usage, as American usage favors shortening words and phrases whenever possible.